I. Project OverviewSeismic design procedures in place for precast concrete diaphragms are currently under reexamination

[Cleland, 2000], largely driven by poor performance in recent earthquakes [Iverson & Hawkins, 1994]. While modifications to diaphragm design have occurred in subsequent code editions, e.g. 1997 UBC [ICBO, 1997], it is generally agreed among researchers and practitioners that current design guidelines require significant further improvement [Nakaki, 2000]. Accordingly, the Precast/Prestressed Concrete Institute (PCI) has issued an RFP for the development of a proper design methodology for precast concrete diaphragms. This proposal is a response to that RFP from a university consortium research team representing the Unversity of California San Diego (UCSD), Lehigh University (LU) and the University of Arizona (UA).

The team proposes a comprehensive research plan to meet the objectives of the RFP. The effort will be supported by close industry oversight and expertise in the planning, execution and interpretation phases through an active Industry Advisory Panel (IAP). The team will find effective and economical means for the seismic design of precast concrete diaphragms using an integrated experimental/analytical approach in which the experiments at the structural system level (UCSD) and the detail level (LU) are bridged by analytical work (UA). This approach is shown schematically in Figure 1. The IAP will guide the selection of prototype structures, floor plans and reinforcement details to define the physical scope of the study. Experimental evaluations of the design capacity for key regions of topped and untopped precast diaphragms will occur through testing the selected reinforcement details in portions of precast units at full-scale and entire precast units at full-scale (hollow core) and half-scale (double tees). These tests will occur in a single, versatile multi-component load frame being developed at LU. While the application of standard cyclic load patterns will be part of this testing program, a key feature of the research is the use of the companion analytical program at UA to determine load combinations and load histories that more closely represent the actual demands the reinforcing details undergo in an earthquake. The load histories reproduced in the LU multi-component load frame will represent the most critical conditions observed in the analyses of diaphragms in the prototype floor plans under different lateral loading directions. Furthermore, the demand levels needed to interpret the LU experimental results will be provided by earthquake simulations (nonlinear dynamic analyses) of the prototype structures conducted at UA and UCSD. Further distinguishing this program from any previous effort in this area is the verification of the analytical modeling through experimentation (quarter-scale quasi-static and shake-table dynamic system tests with full diaphragms at UCSD).

The research program is structured to produce distinct design deliverables including: (1) an appropriate diaphragm design force pattern in terms of magnitude and distribution; (2) a procedure to determine the likely combination of internal forces at key diaphragm sections; (3) a unified design for reinforcement in untopped and topped diaphragms; (4) structural integrity provisions including the required ductility characteristics of the reinforcement; (5) the strength and ductility characteristics of typical diaphragm reinforcement and connection details relative to these provisions, including prequalification of existing details and a prototcol for qualification testing for new details; (6) design and detailing recommendations for anchorage of the diaphragm to the vertical elements of the lateral (load-resisting) system; and (7) diaphragm elastic stiffness calculations and limits on diaphragm flexibility. These deliverables will address industry concerns with current ACI 318 design provisions, current diaphragm design force levels, and displacement compatibility issues.

II. Issues in the Development of a Design Methodology for Precast Concrete DiaphragmsThe critical steps involved in an adequate seismic design for precast diaphragms include:

(1) Properly estimating the diaphragm design forces;(2) Determining the internal force path these loads take within the diaphragm and:

(i) providing elements to transfer these forces across joints between precast units;(ii)providing adequate anchorage to the vertical elements of the lateral system.

(3) Sustaining the diaphragm’s structural integrity in extreme seismic events including providing:

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Figure 1. Diagram of Research Coverage.

(i) adequate ductility to critical reinforcement (and adequate seating to the precast units).(4) Limiting diaphragm flexibility to avoid large story drifts causing collapse in a severe earthquake.

Each of these design steps has certain challenges associated with them. These challenges are largely due to the complex behavior of floor diaphragms themselves, and the dependency of diaphragm performance on interrelated behavior from the structural system level to the reinforcing detail level. Shortcomings in the current design can be traced to inadequately addressing these issues. This section elaborates on these issues. Each discussion culminates with a summary on: (i) implications for design practice; (ii) proposed code changes to advance design practice; and, (iii) the research activity needed to arrive at that code change:

(1) Estimating Diaphragm Design Forces – Diaphragm design forces are currently obtained through an equivalent lateral force (ELF) procedure. Figure 2a, for instance, shows the ELF pattern providing the UBC diaphragm load Fpx. As almost all subsequent diaphragm design steps depend on the value of Fpx, one would hope that these design forces bear a resemblance to the inertial forces that actually develop in floor diaphragms during seismic events. However, evidence exists to show that the design code ELF values may in cases significantly underestimate diaphragm inertial forces [Rodriguez, Restrepo and Carr, 2002] including the possibility of extreme load events [Fleischman and Farrow, 2001]. Furthermore, the maximum forces can occur at lower regions of the structure [Fleischman, Sause and Pessiki, 1998; Rodriguez, Restrepo and Carr, 2002], in direct contradiction to current ELF patterns (See Fig. 2b). Large diaphragm forces have been deduced from floor acceleration measurements in actual structures during earthquakes [Hall et al., 1995] and in shake-table tests [Kao, 1998].

Figure 2. Diaphragm Load Distributions: (a) Code Design ELF; (b) Typical Analytical Results.

Implications for Design Practice : (1) The diaphragm equivalent lateral force pattern (Fpx) cannot be relied upon for accuracy in its current form; (2) The potential for extreme diaphragm force severely impacts the ability to develop a reliable and economical prescriptive elastic design approach.Proposed Design Practice Advances: (1) Develop new diaphragm design forces based on a more appropriate pattern and the use of overstrength factors; (2) Promote elastic response, but be prudent in anticipating unintended ductility demand.Required Research Activity: Determine likely diaphragm force demand by performing dynamic analyses on a representative set of precast structures under ground motions scaled to hazard levels for different regions of the country (UA, UCSD). Verify the analyses through shaking table test comparisons (UCSD). Industry Advisory Panel (IAP) Contribution: Guide the selection of representative structures in terms of: (1) lateral system types; (2) story height (3) floor plan – dimension and lateral system layout.

(2) Determining Diaphragm Internal Force Paths – The design of precast diaphragm systems requires adequate reinforcement to transfer the diaphragm internal forces across joints between the precast units. This statement holds true for topped floor systems as well as untopped since, as stated in the RFP, the topped system is likely to crack along the edge of precast units. Diaphragm reinforcement quantities are

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typically determined using a horizontal plate girder analogy [Bockemohle, 1981]. In this procedure, the diaphragm is treated as a simple beam lying on its side to determine the internal actions of moment and shear due to Fpx (See Fig. 3a). Reinforcement details take on different forms depending on the type of precast unit and construction, but in general: chord steel is provided to carry the entire in-plane bending moment; web reinforcement across panel joints parallel to the seismic load is designed to carry the entire in-plane shear; collector steel is provided at the points where the diaphragm connects to the vertical elements of the lateral system. If joints transverse to the loading direction exist, reinforcement is provided across these sections in accordance with tributary shear guidelines [PCI, 1999]. There are a number of difficulties with using the horizontal plate girder approach for precast systems, most notably that the method counts somewhat on plastic redistribution to allow the forces to end up as shown in Fig. 3a; actual force paths will instead follow stiffness. Precast diaphragms in their current form have little inherent

plastic redistribution qualities, and thus if a section along the stiffness path cannot accommodate the forces, a nonductile failure is the likely result. These ideas are developed in the following:

(i) Force transfer across joints : In Figure 3a, Region 1 represents a portion of a rather simple floor diaphragm in which the web reinforcement, designed simply for shear transfer, is under high tension due to the in-plane bending of the diaphragm. One could argue that this unaccounted tension force occurs at a point of zero in-plane shear and although not designed for tension, the web reinforcement might possess enough inherent tensile strength to handle this force. However, many diaphragm joints are subject to complex force combinations (shear, moment, and at times axial force coinciding at a section) that are more demanding than the internal forces determined from the simple-beam treatment of the horizontal plate girder model in Figure 3a. Take for instance Region 2, where we assume sufficient weak-axis flexibility in the shear wall to produce the moment diagram shown, i.e. zero diaphragm (in-plane) moment at the boundary. This condition is not necessarily always present, consider for instance the cases shown in Figure 3b in which maximum shear and non-negligible moment coincide. Consider now region 3, in which the reinforcement is treated as resisting only tributary shear; this will be the likely outcome if the inertia forces shown travel sideways to the collector steel; however a stiffer load path might exist directly into the precast floor beam causing a shear-tension combination on the tributary steel. In addition to these cases, other conditions contribute to force combinations including the direction of attack of lateral inertial loads (i.e., transverse, longitudinal or diagonal) and internal forces due to differential movement of vertical elements of the lateral system (See Fig. 3c). Design procedures currently do not account for these force combinations. Furthermore, complex force paths can develop due to irregularity in the floor plan (See Fig. 3d). Codes in other countries, e.g. the NZS 3101 [Standards New Zealand, 1995],

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require a rational analysis to design and detail internal force paths for diaphragms with openings or irregular floor plans, recommending the strut-and-tie approach [Schlaich et al, 1987].

Implications for Design Practice: (1) The commonly accepted horizontal plate girder analogy that treats the chord and web reinforcement internal forces as independent items is inadequate for use in precast diaphragms; (2) Diaphragm reinforcement based on simple beam moment and shear diagrams can be insufficient due to the presence of force combinations due to loading direction and diaphragm geometry.

Proposed Design Practice Advances: Develop a simple yet effective method of calculating chord and web forces at a section based on the relative stiffness of diaphragm reinforcement elements. Provide guidance to the designer on how to determine and combine shear and tension components in the analysis of floor systems to permit the design of reinforcement for resultant forces. Promote the use of rational methods, e.g. strut-and-tie or stringer-panel methods [Blaauwendraad, Hoogenboom, 1996] for irregular floor plan cases.

Required Research Activity: Determine the likely: (i) force distribution between chord and web reinforcement for different details at a general section; (ii) force combinations at critical sections of different representative floor plans; and (iii) chord-collector interaction for different seismic loading directions. These objectives will be accomplished by performing finite element analyses on a set of representative precast floor plans and details under lateral loads from different angles of attack (UA). These analyses will be verified by a limited number of quasi-static diaphragm tests and shake table tests that reproduce the diaphragm’s distributed horizontal geometry (UCSD). The resulting force combinations will be used as loading histories for the full-scale experiments in an efficient load frame to allow several details and locations to be evaluated under an accurate representation of actual force conditions (LU). IAP Contribution: Guide the selection of representative floor plans in terms of: (1) configuration – dimension, framing and lateral system layout; (2) reinforcement details and construction practice. Work with the research team to determine strategies to include rational design methods into building codes.

(ii) Anchorage to lateral system: The anchorage details connecting the diaphragm to the lateral system must transfer the inertial forces throughout a seismic event. Accurate force demands (Steps 1 and 2-i) are therefore essential. However, it is also important to account for secondary effects including superimposed gravity loads and imposed deformations from vertical elements of the lateral system [Menegotto, 2000]. Detailing provisions should ensure adequate deformation capacity of the diaphragm connections to account for these out-of-plane effects in conjunction with the in-plane force paths [Bull, 1997]. Furthermore, the floor system’s vertical geometry is also important in determining the load path as several types of precast components with different centroidal heights are joined by a combination of mechanical and bearing connections eccentric to the plane of the diaphragm.

Implications for Design Practice: The design of the diaphragm anchorage to the vertical elements of the lateral system must account for, in addition to large floor forces and internal force combinations, the floor deformation compatibility with the lateral system and eccentricity in vertical profile of the floor system.Proposed Design Practice Advances: Develop a design calculation for diaphragm anchorage that uses a separate overstrength factor to account for the additional demands at these locations. Provide detailing requirements to assure accommodation of lateral system imposed deformations.Required Research Activity: Perform a limited number of quasi-static diaphragm tests and shake table tests on specimens that reproduce the diaphragm’s vertical profile, anchorage to the lateral system elements, and out-of-plane actions of the lateral system (UCSD). Verify findings through 3D finite element analysis of the floor diaphragm anchorages to include gravity load and other out-of-plane actions (UA).

(3) Maintaining Structural Integrity – In the event of an overload (a general concern in seismic resistant design, but a particular concern here given the potential for unexpectedly large floor inertial forces), the diaphragm will undergo inelastic behavior. In many types of floor systems, a casual treatment of this behavior may be forgiven as the floor can be assumed both rigid and capable of transferring inertial loads through a short path.. However, the paneled nature of the floor system combined with relatively large spans between collecting elements does not provide inherent protection against overloads, and the diaphragm may become the critical component of the lateral system. Thus, structural integrity measures must be designed into a precast diaphragm, even if the intent is an elastic diaphragm design.

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(i) Detailing for ductility: The paneled nature of the floor diaphragm will tend to concentrate the inelastic deformation demand in the reinforcement within joints between precast units. The reinforcement details were developed without full consideration of ductility requirements. Indeed, a nonductile failure mode (shear failure of the web reinforcement) is the likely controlling limit state in the event of inelastic diaphragm action [Farrow and Fleischman, 2002]. The potential for this failure mode must be eliminated. A complication in detailing to avoid the shear failure is the tensile deformation demands placed on the web reinforcement in high in-plane bending regions (e.g. region 1 in Fig. 3a). These demands presumably concentrate at column lines where spandrel beams terminate, and can become significant if the chord steel yields (with a distinct possibility of buckling in a subsequent semi-cycle). Standard web reinforcement (welded wire fabric and mechanical connectors) possesses limited tensile deformation capacity and thus may fail in tension.

Diaphragm detailing issues take on an added level of complexity for irregular floor plans. As an example consider the parking structure diaphragm, an irregular floor plan studied extensively by members of the research team. A typical parking structure diaphragm exhibits at least four failure-critical locations, one of which will control depending on the loading direction and lateral system layout. Figure 4a shows examples of the complex deformation patterns that can develop under different loading conditions. Not only will these floor deformations create force combinations, the discretely-connected precast units themselves can develop complex deformation patterns. The panel joints will not necessarily follow plane-sections assumptions, particularly if portions of the web reinforcement are lost (See Fig. 4b). Therefore, forces acting on individual reinforcing details may not always be accurately predicted by calculations based on P/A, Mc/I and VQ/I, even if the internal force combinations (P,V,M) are accounted.

Implications for Design Practice: Detailing of the connections in diaphragms is one of the most crucial aspects in ensuring adequate seismic performance. Given the uncertainties in loading it is paramount that connections posses significant ductility capacity to enable redistribution of internal forces. The current state-of-practice may not include reinforcing details that meet the required characteristics and thus new details may need to be developed. Proposed Design Practice Advances: Develop a rational and unified method for treating reinforcement elements including: (1) Eliminating the potential for nonductile failure in a diaphragm overload situation by providing a capacity design for web reinforcement with respect to the chord steel; (2) Providing recommendations for the tensile characteristics of web reinforcement (strength, ductility or compliance) to provide the desired seismic behavior; and (3) maintain composite action between the topping and the units.Required Research Activity: Investigate deformation patterns and ductility demand in the shaking table tests (UCSD). Examine regular to irregular floor plans analytically to determine characteristics of local deformation demand on details (UA). Perform load tests for key regions of each set of representative floor plans using the load patterns obtained in analysis to produce likely overload (ductility) conditions (LU). Investigate bond strength between topping and the precast units (LU).

(ii) Seating: Diaphragms must also preserve adequate seating for the precast units to maintain gravity load carrying capacity during an earthquake, including accounting for displacements and forces imposed on the diaphragm by the relative motion of the lateral system elements. A considerable amount of research has occurred in this area [Herlihy and Park, 2001] including the development of new details

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Figure 4. Irregular diaphragm response: (a) different loading conditions; (b) panel deformation patterns.

[Mejia-McMaster 1994]. Seismic codes have developed structural integrity provisions, e.g [ACI, 1993]. Thus, investigation of seating loss will only be considered indirectly within the scope of the research.

(4) Limiting Diaphragm Flexibility – Precast construction is commonly and effectively used for building systems with long floor spans. In these structures, the typical distances between vertical elements of the lateral system creates a demanding condition for the diaphragm, not only in terms of generating significant in-plane bending moments and shear forces during seismic events, but also in producing a diaphragm that is quite flexible. Diaphragm flexibility due to the long floor spans is exacerbated by the fact that paneled diaphragms are inherently more flexible than their monolithic counterparts. Members of the research team have performed extensive research on long span systems [Fleischman and Farrow, 2002] [Fleischman et al, 2002] [Fleischman, Sause and Pessiki, 1998]. Conclusions appear below.

Implications for Design Practice: Diaphragm strength factors are required that capture the interrelation of diaphragm flexibility and strength in describing the seismic performance of long floor span structures. The elastic contribution of the diaphragm must be included for lateral-systems that are drift controlled. A restriction is required on building certain configurations, comparable to the longest span parking structures of recent construction, as no design strength increase exists to realize adequate drift performance. Proposed Design Practice Advances: Incorporate a rational deflection calculation in diaphragm design. Restrict diaphragm flexibility within limits that ensure safe drift performance in a seismic event. Account for diaphragm flexibility effects on other performance quantities, e.g. load levels or ductility demand.Required Research Activity: Perform dynamic analyses on a set of prototype structures under ground motions representative of hazard levels for different geographical regions to determine likely diaphragm-induced drift demands (UA). Verify these analyses with a limited number of shaking table tests (UCSD).

III. Concept of the Proposed ResearchIII.1 Rationale – Some of the research activities required to address issues associated with the four

design steps in the previous section have been undertaken previously, by others [Wood et al, 2000] [Wood et al, 1994], and by members of the research team (See nine references in Appendix A). While these efforts have produced valuable information, this previous research suffers from a limitation that diaphragm forces and force paths have been estimated entirely through analytical simulation. These analytical simulations themselves depend heavily on tests of individual reinforcement details under highly idealized loading conditions.

These tests of individual reinforcement details, e.g., [Mattock, 1975], [Pinchiera et al, 2000] [Oliva, 1998], achieved their objectives, and the resulting data has been extremely valuable, providing a basis for analytical models and the capacity of individual details. However, direct extrapolation of these test results to estimate the capacity of an entire joint is questionable, because these details possess limited ductility and act in parallel. Because of this, actual joint behavior depends on a complex interaction of the force combinations, the load history, and the state of other reinforcing details in the joint (intact, softening, failed). In reality, each individual reinforcement detail is subjected to a different force combination (e.g., tension/shear, compression/ shear), and this force combination changes as the stiffness and strength of nearby reinforcement details degrade. Therefore, even the recent ambituous tests of connectors in combined shear and tension [Pinchiera et al, 2000] cannot be extrapolated to accurately predict diaphragm joint behavior.

Entire joints between precast units have been tested [Moustafa, 1981], [Porter and Sabri, 1990], [Menegotto, 1994]. The test setups – typically full-scale precast concrete panels loaded with single actuators – impose artificial boundary conditions (rigid planes, equal displacement constraints, etc.) that limit the extent to which the observed behavior represents the actual behavior of a diaphragm joint. The joint deformation patterns determined by recent analytical studies (e.g., Fig. 4b) suggest that tests using these artificial boundary conditions provide unrealistic estimates of the capacity of the entire diaphragm joint, and the force/ductility demands that occur on the reinforcement details. For this reason, a test program that consists only of tests of full-scale panels with joints under simple boundary conditions is not proposed here, as these tests do not capture all the conditions to which the diaphragm joints are subjected. However, such tests could be used to assist in interpreting the more complex load cases, and a limited number of these tests will be included here as “baseline” tests. Recent tests have attempted load paths under more accurate displacement fields [Herlihy and Park, 2000]. However, the most direct approach is to apply accurate joint forces in the sequence, magnitude, and proportion they occur in analyses of the diaphragm. This is the main concept of proposed research.

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Ideally, one would build a test setup with numerous actuators providing multi-point loading on precast diaphragm subassemblies (shown subsequently in Figure 6), thereby reproducing the force combinations and joint deformation patterns observed in analyses at full-scale for the entire joint. However, for the large number of important parameters being considered in the RFP (topped/untopped; hollow core/double tee; chord, collector, web reinforcement; anchorage, etc), this approach is not economically feasible (it may be in future work – See Sec. III.3). Instead, a versatile load frame is required to test the needed permutations of parameters; yet this load frame must enable tests that provide insight into joint behavior under actual conditions.

Thus, a key feature of the proposed research is the use of a versatile load frame that not only can apply standard load components but load combinations; and the use of detailed finite element (FE) models of complete diaphragms to perform analyses under several lateral loading conditions to determine the critical loading history to apply to reinforcing details (either at full-scale for portions of a panel joint or at half-scale for entire joints). A second groundbreaking feature of the research is that although the project relies, as in previous efforts, on finite element analyses of precast diaphragms, these analyses will be verified by system-level experiments, both quasi-static tests of diaphragm joints and shaking table tests of the entire structure.

III.2 Proposed Integrated Analytical/Experimental Approach - Figure 5 shows a flow chart describing the integrated approach the team proposes for the diaphragm research. The Industry Advisory Panel (IAP) will be instrumental in all phases including at the front end to guide the physical scope (structures, plans, details) and at the back end to facilitate transforming research results into a usable design methodology.

(1) Individual reinforcement detail (element) tests will be performed on needed details (those selected by the IAP but not previously tested) at full scale under simple (proportional) cyclic load combinations. The properties determined (from both prior work and those conducted as part of this program) will be used as input to create accurate diaphragm FE models.

(2) The diaphragm FE models created for representative floor plans (as selected by the IAP) will be analyzed under different earthquake loading conditions. The analytical models will be verified or appropriately modified by direct comparison to quasi-static push tests (2a).

(3) Earthquake simulations will be performed on models of representative structures at different levels of seismic hazard. These analyses will be verified or appropriately calibrated by shaking table tests (3a). The analyses establish seismic demands.

(4) Based on seismic demands obtained in the structure analyses in (3), and force combinations and deformation patterns obtained in the diaphragm analyses in (2), realistic loading patterns are applied to portions of full-scale precast units and entire joints at half-scale in the multi-component load frame. These patterns will correspond to histories at different critical diaphragm locations (maximum flexure, shear, adjacent to wall anchorage, etc.).

III.3 Future Opportunities - The consortium-based approach outlined in the PCI RFP provides a natural application for pursuing integrated experimental/analytical research, and therefore represents the best opportunity thus far to develop comprehensive understanding of diaphragm behavior. For this reason, the design methodology emerging from the PCI-funded research should represent a significant advance over the state-of-the-practice. However, it is envisioned that diaphragm research will still be needed in the future to further our understanding of the topic; increase the confidence in the design methodology developed by the PCI research; point to areas that require modification, and aid in the development of new systems or construction techniques, particularly those brought on by the new design methodology.

In this regard, the timing of the PCI RFP is ideal because the proposed project timetable coincides with the construction and commissioning of the George E. Brown Network for Earthquake Engineering Simulation (NEES). Given the expected capabilities of the NEES Portfolio, including large scale shaking tables and full-scale hybrid testing (experiments interacting with analysis), the prospects of a new generation of structural system experimental research is high. NSF plans to fund NEES research at nearly $300M during

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Figure 5: Flow chart of integrated experimental and analytical activities at the three consortium sites.

FYs 2004-2014. The seismic performance of precast diaphragms is an ideal candidate for this program: NEES testing facilities will be able to accommodate the distributed nature of the floor system in near full-scale, enforce realistic boundary conditions, and provide a truer representation of the actual dynamic loading, all significant issues in attempting to accurately capture the behavior of precast floor diaphragms.

The research team is well-represented in NEES, including the award for the largest domestic shaking table (UCSD) and a full-scale hybrid testing site (LU). The team’s position within NEES creates the likelihood that experimental research on diaphragms can continue following successful completion of the PCI research. As the NEES Network will greatly extend possibilities for diaphragm experimental research, the team views this as an important potential step. As an example of future work, Figure 6 shows a test frame capable of reproducing deformation patterns from analyses or shaking table tests on full-scale precast panels. This objective is accomplished through an array of distributed actuators, thus accurately representing capacity and realistic simulating demand over the entire precast joint. This multi-point load frame would be capable of testing entire precast panels or bays under the actual single and double curvature displacement patterns producing realistic combinations of shear, axial and flexural loads. Such a setup could be used to perform “proof of concept” tests on full-scale precast units designed using the emerging design methodology.

Figure 6: LU Multi-Point Load Testing setup for proof of concept testing: (a) single curvature; (b) double curvature.

IV. Research ProgramThe analytical program will rely on the team’s advanced state of knowledge on this topic to extend rather

than develop models. The experimental program will make use of existing infrastructure at the UCSD and LU testing laboratories. Preliminary design of these test setups has already been initiated. In particular, it is important to note that the team member leading the shaking table program has performed nearly identical tests on another type of construction [Filiatrault, 2002], and that these tests are being heavily leveraged by one of the consortium institutions (UCSD). All these factors tend to minimize risk and start-up delays. This is viewed as a significant advantage to allow the team to focus their creative energy on the research and design issues.

IV.1 Description of Analytical MethodsModeling the behavior of precast floor diaphragms is challenging, requiring detailed models to

capture complex deformation patterns, compatibility-induced forces and non-traditional dynamic mode shapes. Thus, the endeavor requires realistic models that capture pertinent behavior through the use of the latest analytical tools and computational power, and must not only involve competent modeling (both nonlinear static and dynamic), but also advanced understanding of the modeling issues. At the same time, it must be kept in mind that simple tools and models need to be developed for practical use in design.

The approach adopted in the team’s prior research, detailed finite element models of individual floor diaphragms and transient dynamic analysis of structures, will be extended here. The models will be built using empirical data from tests on reinforcing elements. These models will be subjected to nonlinear static (pushover) analyses to determine the diaphragm service level stiffness and ultimate strength for different structural dimensions and construction details. Multi-degree-of-freedom (MDOF) models of the protoype

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structures (at less detail to facilitate reasonable analysis times) will be created based on the properties derived from the pushover analyses. The MDOF models will be subjected to suites of earthquake ground motions through nonlinear transient dynamic analysis to establish seismic demands for different representative structures. The team will evaluate the feasibility of three-dimensional nonlinear dynamic analysis, and though its use certainly would enhance the work, the ability to perform the research does not hinge on this feature.

IV.2 Description of Structural System/Diaphragm Experimental ProgramA three-story one-quarter scale building will be built at UCSD. This building will be constructed to

observe system behavior under static and dynamic loading conditions. The plan dimensions of the building will be 6 ft 6 in. wide by 19 ft 6 in. long, as shown in Figure 7a. The diaphragm in this building will be constructed using scaled precast concrete floor units and will incorporate connection details identical to those used in practice. The diaphragm reinforcement will be designed in accordance to the requirements of the 1997 edition of the Uniform Building Code [ICBO 1997]. One floor will incorporate a untopped diaphragm whereas a cast-in-place topping will be featured in the other two floors. Floor units of different widths will be used to build each of the topped floors to represent 3 ft double-T units or 4 ft hollowcore units.

The building will be constructed on the 10 ft by 16 ft uni-directional earthquake simulator facility at the Charles Lee Powell Laboratory. Structural walls will provide the lateral force resistance in the direction of loading. The walls will be supported on a stiff steel base with cantilever outriggers. A similar base was successfully used recently to test a full-scale woodframe house [Fischer, D. et al. 2000; Filiatrault et al. 2002].

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Figure 7: a. Diaphragm Plan View for UCSD System Test; b. Quasi-static Testing of 3rd Floor Diaphragm.Characterization of the building and diaphragm’s response will be obtained through quasi-static and

dynamic shake table tests. The quasi-static tests will consist on the application of a point load at the center of a diaphragm to about 75 percent of the in-plane load capacity. For this purpose, the floor diaphragm under consideration will be attached to the reaction wall that is adjacent to the shake table, as shown in Figure 7b. The base of the building will be moved slowly by the shake table in order to induce the desired loading to the diaphragm. Each diaphragm will be subjected to three complete cycles to 25, 50 and 75 percent of the theoretical in-plane capacity. Displacement transducers will be set in place to monitor the diaphragm in-plane deformations and to enable the decomposition of the shear and flexural deformations. Strains in different parts of the diaphragms and in the main reinforcement will also be monitored during these tests. The main advantage of this quasi-static testing technique using the complete structural system is the direct inclusion of realistic boundary conditions along the edges of the diaphragms. The ensemble of records for the tests will include pulse-loading, band-limited white noise and historic ground motions, including a near-fault record.

IV.3. Description of Precast Units/Joint Reinforcement Detail Experimental Program A multi-component diaphragm (MCD) test fixture will be built at LU. The MCD testing will

investigate a variety of precast diaphragm joint reinforcement details at full-scale including connections

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between individual precast units, connections between precast units and intermediate supports, and connections between precast units and collectors such as shear walls (See Fig. 8). These tests will enable direct evaluation of a detail’s ability to transfer joint forces, provide adequate anchorage to the vertical elements of the lateral system, and sustain the diaphragm’s structural integrity in extreme seismic events.

The majority of testing will focus on the performance of the connected precast units subjected to a combination of shear, axial load, and flexure across key portions of joints between precast units (Fig. 9a). The system will allow testing of conditions at walls or supporting beams (See Fig. 9b). Finally, entire panel joints will be tested for reduced-scale double tees units and full-scale hollow core units (See Fig. 9c). Test sub-components will measure approximately 20ft. x 20ft. in plan. The setup will be configured to accommodate both these types of units with and without topping slabs and apply cyclic loading at quasi-static displacement rates. Topped tests will be staged to capture the in-service state and gravity load.

C. Intermediate Diaphragm Support

B. Diaphragm - Wall 1A. Diapragm (Panel to Panel Interaction)

E. Diaphragm - Wall 3

D. Diaphragm - Wall 2

FLOOR PLAN

Figure 8: Examples of locations in precast diaphragms to be reproduced in the MCD testing.

The MCD fixture will first be used to evaluate elements or panels under simple demands such as pure shear or axial load (baseline tests). The purpose of these tests is to provide a performance baseline for the subsequent precast joint tests under more complex loading conditions. An example of a representative baseline study the IAP might consider is the examination of welded wire fabric shear friction capabilities under cyclic shear load as superimposed tension (or flexure) is increased.

Figure 9: Plan views of MCD fixture showing test configurations A,B,C.

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A. Diaphragm panel-panel connection

B. Diaphragm - wall or intermediate support

C. Scaled diaphragm panel-panel connection

WWF ChordSteel

Shear Actuator

Beam orWall

Vertical Actuator

Vertical Actuator

Following the baseline experimental program, tests will be conducted using histories of varied levels of axial, shear, and moment determined in the analytical program to define the forces and displacements imposed by the three actuators of the MCD fixture. These tests will evaluate performance under more realistic load histories. For scheduling efficiency, hollow core tests will be conducted in first followed by the double tee investigation. The scheduling plan is summarized in section 5. Though the test matrix will be developed in collaboration with the IAP, Table 1 shows a potential testing program involving approximately 16 full-scale

reduced length precast unit test specimens.Table 1: Potential joint/unit test matrix.

V. Schedule of Work As requested in the RFP, the program is scheduled in a planning stage (Phase I) and a research stage

(Phase II). However, certain Phase I “hard” research activities must be performed to meet the RFP objectives within the planned 3-year time frame. Phase I research and planning activities are detailed below. Phase II research tasks will be fully defined during Phase I Research Meetings (RM). However, a general description of Phase II activities also follows. The activities described are based on a December 2002 award announcement.

The common responsibilities of the IAP and the research team include: developing a target design philosophy; determining the physical scope, agreeing to test setups and programs, setting a testing protocol for research and one for qualification; developing performance targets and appropriate metrics, and developing a uniform design methodology for precast concrete diaphragms. These activities will be discussed and planned at biannual Research Meetings. Tasks identified in the RFP regarding development and approval of test setups; and conception and approval of the test program will occur over the first two (Phase I) RMs.

V.1 Phase I Activities Task 1. Submit proposal to NSF GOALI Program – The team anticipates submitting for the February 7 deadline.

Task 2. Assemble Industry Advisory Panel – The research team envisions finalizing the Industry Advisory Panel (IAP) within 4 weeks of notification of the award (See Note A). The IAP will meet with the research team two times annually: once during PCI Committee Days (April) and once during the PCI National Convention (October).

Task 3. Review and evaluate existing code – This step also includes conducting a literature survey of prior research (See Note B); and creating a database of industry and proprietary testing. The code review, literature survey, and database work will be completed within the first two months. Evaluation of existing code will commence at the first RM#1 (See Note C); code evaluation subtasks will be developed and assigned, and consensus on the code evaluation/new directions is targeted for RM#2.

Task 4. Distribute packet for RM#1 – The packet will contain the agenda for the first research meeting and background material including lists of potential structures, floor plans and reinforcement details for study. These options will be discussed and selections will be made for inclusion in the study during RM#1.

NOTES on Phase I initial planning activities:(A) The team has already contacted leading design practitioners in the area including: N. Cleland, S.K.

Ghosh, J. Maffei, and S. Nakaki. These individuals have agreed to participate on the IAP if the LU-SD-UA

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Test Description Load History Test Hollow Core**Configuration Untopped Topped Untopped

Simple Panel-Panel Connection TestsHigh Shear Region Monotonic A A1DU - A1HUHigh Shear and Tension Monotonic A A2DU - A2HUHigh Shear Region Cyclic A A3DU1 & A3DU2 A3DT A3HU1 & A3HU2High Shear and Tension Cyclic A A4DU1 & A4DU2 A4DT A4HU1 & A4HU2

Diaphragm Panel-Panel Connection TestsHigh Flexure Region Cyclic C C1DU C1DT -High shear and Flexure Cyclic C C2DU C2DT C2HU

Multiple Connection Panel-Panel TestsHigh Shear, Tension, & Flexure Region 1 From Analysis A A5DU1 & A5DU2 A5DT -High Shear, Tension, & Flexure Region 2 From Analysis A A6DU1 & A6DU3 A6DT -High Shear, Tension, & Flexure Region 3 From Analysis A A7DU1 & A7DU4 A7DT -

Multiple Connection Panel-Beam Tests*Parking Garage Ramp Interface From Analysis B B1DU - -High Shear Region of Regular Floor From Analysis B B2DU - -

Multiple Connection Panel-Wall Tests*Exterior Wall Cyclic B B3DU - -Interior Wall Cyclic B B4DU - -

* Tests contingent on additional GOALI funding ** D - Double tee, H - Hollow core, U - Untopped, T - Topped

Double Tee**

consortium proposal is successful. This team provides the IAP with significant expertise and broad geographical representation. Other potential members may be identified. Producer members have also been contacted and have agreed to participate in the donation of specimens for both the LU and UCSD tests. See Appendix C for letters of commitment for the PCI-funded portion of the proposed research (M. Bertolini, G. Force, K. Baur).

(B) The members of the research team have published several articles on the topic of precast diaphragms and therefore have obtained, read and referenced most of the existing research on this topic. Two of the members of the research team (Restrepo and Fleischman) are members of the Commission 7 task group, International Federation for Structural Concrete, writing a state-of-the-art report on the seismic design of precast concrete structures and thus have access to recent international developments on precast diaphragm research.

(C) One of the IAP members (Ghosh) is heavily involved in code-related issues including serving on several code-writing committees. Another member (Nakaki) has been involved in code changes for precast diaphragms and has recently written an EERI report that contains a comprehensive summary of these code changes. Another member (Cleland) has been working on producing new seismic design recommendations through his capacity as chairman of the PCI Seismic Committee. Finally, one member (Maffei) serves on ACI 318. Thus, the research team is confident that the industry advisory panel will provide a valuable service in this area.

Research Meeting (RM) #1: PCI Committee Days, April 20031) Familiarize IAP with research team’s proposed approach; review and approve or modify as needed

briefly present update on preliminary designs on LU and UCSD test setups; UA modeling2) Physical Scope

Select set of prototype structures (topped and untopped) floor plans (squat w/internal beam; long single span rectangular; irregular-

parking structure?) – For each, specify hollow core, double tee or both structural systems (wall, frame, other?) number of stories (low-rise to mid-rise?)

Milestone #1: Determine scope of study in terms of structural system and floor plans Select geographical regions (moderate and high seismic zones) Select a set of reinforcement details

For topped/untopped; hollow core/double tee Existing details, promising new details, state of construction in other countries

Milestone #2: Select feasible subset of reinforcement details for the study. 3) Review state of testing on diaphragm reinforcement details

Identify test history on reinforcement details. Identify missing coverage from subset selected in Outcome #2.

Milestone #3: Select (element) testing program for individual reinforcement details.4) Approve element testing program at LU (Phase I)

load combinations shear loading (w/lateral confinement) tension loading; shear and tension combined

loading prototcols monotonic; cyclic (increasing amplitude, constant amplitude?)

5) Present initial plans for UCSD test structure: approve, modify as needed Scope: floor plans, construction (topped/untopped?), details; review/identify producer donations

6) Initiate discussion on design methodology evaluation of existing codes rational methods of analysis and design other (international) codes required features of new design methodology

prescriptive elastic design web reinforcement tension compliance vs. strength performance requirements: ductility, flexibility limits

Task 5. Refine analytical models – Existing analytical models will be extended for use in this research This activity will occur prior to Committee Days so the analytical program can commence directly after RM #1.

Task 6. Perform earthquake simulations on prototype structures – Using selected floor configurations and structural systems, design parametric study for determining system level demands: Rig. Dia-UCSD, Flex. Dia-UA

Select ground motions corresponding to multiple hazard levels for different geography. Select design parameters: Diaphragm strength, flexibility, lateral system strength, etc.

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Milestone #4: Estimate of Seismic Demands on Prototype Structures.Design Deliverable #1: Design Force Pattern; Limits on Diaphragm Flexibility.

Task 7. Baseline Element Tests (LU) - The needed baseline tests on individual elements identified in RM#1 will commence at LU. The purpose of these tests in Phase I is to provide accurate input data for analytical models of the diaphragm. Tests of connections in hollow core panels will be conducted first followed by double tee connections. Tests will consist of single element subjected to combinations of shear, tension, and compression loading.

Milestone #5: Capacity of Individual Reinforcement Details.Design Deliverable #2: Nominal Strength of Individual Reinforcement.

Task 8. Develop UCSD quasi-static/shake table tests – Preliminary work will be performed to assure the UCSD tests will provide the needed data including:

Nonlinear finite element analyses of the quasi-static tests (UA) Dynamic analysis of the shake table tests (UCSD) Tentative decision on the final test specimens (pending IAP approval in RM#2)

Research Meeting #2: PCI Convention, October 20031) Report on GOALI funding2) Report on research progress

Analytical - Seismic Demands on Prototype Structures Experimental - Capacity of Individual Reinforcement Details

3) Revisit Selection of Reinforcing Details approve; improve; reject; Design of Prototype Structures (to current code)

4) Finalize UCSD test program quasi static loading, shake table histories review expected performanceMilestone #6: Approve UCSD program; release producers to create specimens

5) Propose LU multi-component test program Use analyses to guide Estimate number of tests

Breakdown among panel to panel; panel to wall/frame; panel to beam6) Design Methodology

Propose load pattern (initial) Propose drift limits

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Task 9. Deliver Interim Report - Present outcome of Phase I work at 2003 PCI Convention; provide written report in November 2003 (includes milestone in RM#2). PCI approves/modifies the testing program December 2003.

5.2 Phase II Research TasksAs Phase II is initiated, three parallel activities will occur at each consortium institution:

Task 10a. Perform Diaphragm Analyses (UA) - Diaphragm analyses are performed on detailed finite element models representing the prototype floor plans under the demands established in the earthquake simulations of the prototype structures (Phase I, Task 6). The models will be built with the information provided in Task 7 and loaded to levels observed in Task 6.

Prototype floor configurations Topped/pretopped; Hollowcore/double tees Pushover; cyclic, Earthquake histories

Task 10b. Perform Diaphragm/Structural System Level Experiments (UCSD) - Quarter-scale models of the topped and untopped prototype diaphragms will be evaluated under quasi-static testing and shaking table tests.

Task 10c. Multi-point Load Verification Testing (LU) - System tests will be conducted on full-scale panels. The system behavior of the panels will be evaulated using the load histories from the most demanding situation (high shear/flexure/axial in parking structure).

Research Meeting #3: PCI Committee Days, April 20041) Report on Research Program: UCSD, LU, UA2) Select loading conditions for LU multi-component tests (based on FE results to date)

Floor Plans: Key Floor regions Loading – Orientation, intensity level, etc.

Milestone #7: Finalize the LU multi-component program

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Task 11: Compare to shaking table results - The topped shaking table tests and the FE analyses will be compared and evaluated. Milestone #8: Decide on the load patterns/histories for use as input to the MCD.

Task 12: Multiple Connection Panel-Panel Experiments (LU) – Tests on full-scale reduced length panels with multiple connections will be conducted. The MCD will simulate the displacement demands on the connections found by the analytical and shaking table tests.

Research Meeting #4: PCI Convention, October 20041) Report on Final Baseline Tests; Initial Multi-component tests2) Develop quantification metricsMilestone #9: Develop Target Demands; Design Deliverable: Baseline Joint Capacity

Research Meeting #5: PCI Committee Days, October 20041) 1st draft design methodology: Design Deliverable: method of analysis for force combinations2) Qualification testing protocol; Design Deliverable: Baseline Capacity of Joint

Task 13: Full Panel Verification or Panel-Wall/Beam Experiments – Contingent on additional funding and the results of the earlier analyses and experiments either system verification tests or panel to lateral resisting system tests will be conducted. System verification tests will be performed on full-scale panels using the Multi-Point Load Testing setup. The panels will be designed using the design methodology and subjected to load histories from the most demanding situation (high shear/flexure/axial in parking structure). The load histories will reproduce the single and double curvature exhibited by these panels during diagonal. The panel-wall or panel-beam tests will evaluate the performance of diaphragm to lateral resisting system connections. These tests will be conducted on full-scale reduced length specimens using the MCD test fixture. Design Deliverable: Ductility Demands on Details

Research Meeting #6: PCI Convention, October 20051) Design Deliverable - Final draft design methodology: 3) Design Deliverable - untopped applicability

VI. PersonnelRobert B. Fleischman is an Assistant Professor in the Department of Civil Engineering and Engineering Mechanics at the University of Arizona. Dr. Fleischman obtained his Ph.D. from Lehigh University, followed by a PostDoc under R. Sause and S. Pessiki on an NSF-funded study of precast diaphragm failures in the 1994 Northridge Earthquake. This work has been referenced in both the 1997 FEMA-273 Guidelines and the 2000 NEHRP Code. Dr. Fleischman received the 1996 PCI Daniel P. Jenny Research Award to study the seismic behavior of precast parking structure diaphragms. Dr. Fleischman has published 5 journal articles, 2 conference proceedings and a chapter in a state-of-the-art report on this topic and on flexible diaphragms in general. Dr. Fleischman has also lectured on the Seismic Rehabilitation of Concrete Buildings for the 1998-99 Short Course: Emerging Developments in Earthquake Engineering. Dr. Fleischman is a NSF Faculty Early CAREER Awardee, and a member of the Earthquake Engineering Research Institute (EERI), the Seismic Effects Committee of ASCE; the Seismic Design Working Group, Committee 7 of the International Federation for Structural Concrete (FIB), and the PCI Seismic Design Committee.

Jose I. Restrepo is an Associate Professor and Associate Director of the Charles Lee Powell Laboratory in the Department of Structural Engineering at the University of California, San Diego. Dr Restrepo obtained his Ph.D. from the University of Canterbury, New Zealand with a thesis entitled “Seismic Behaviour of Connections Between Precast Concrete Elements” supervised by Prof. Robert Park. While being a Senior Lecturer at the University of California, Dr. Restrepo was largely involved with research into the seismic response and design of precast concrete systems. In 1998 Dr Restrepo was the recipient of funding from the Ministry of Science and Technology of New Zealand to investigate the Seismic Resistance of Precast Concrete Systems. Dr Restrepo had active links to the New Zealand industry before moving to California in 2001 and was a Member of the Council of the New Zealand Concrete Society. Dr Restrepo has published 16 papers in peer reviewed journals and gave a Keynote address on the First fib Congress held in Osaka in October 2002. Dr. Restrepo is a member of the PCI Seismic Design Committee and Seismic Design Working Group, Cmte. 7, International Federation for Structural Concrete (FIB).

Clay Naito is an assistant professor of structural engineering at Lehigh University and a licensed P.E. in California. He earned his Ph.D. (2000) and M.S. (1994) degrees in Civil Engineering from the UC Berkeley and his B.S. (1993) degree from the University of Hawaii. Dr. Naito’s research areas include earthquake engineering of concrete and wood frame structures, performance of FRP materials, and nonlinear finite element evaluation of reinforced concrete structures. He has significant experience with experimental testing and analysis of large-scale structures and structural components. He has conducted a number of seismic research investigations including quasi-static testing on reinforced concrete bridge beam-column connections, waffle slab building systems. As a visiting researcher at PWRI in Japan he worked on dynamic testing of steel reinforced concrete bridge columns, and as a post-doctoral researcher at UC Berkeley he coordinated the full-scale shake table tests of a three-story woodframe apartment building. Clay is an active member in ACI committee 369 Seismic Repair and Rehabilitation.

Andre Filiatrault is a Professor in the Department of Structural Engineering at the University of California, San Diego. He earned his PhD degree at the University of British Columbia, Vancouver, Canada. Dr Filiatrault’s research areas include

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Earthquake Engineering of Structural and Lifeline Systems. Dr Filiatrault has conducted a large number of Shake-table experiments in a variety of structural systems and materials. He was a Co-Investigator for the CUREE (Consortium of Universities for Research in Earthquake Engineering)-Caltech Woodframe Project, which included the nation's first full-scale dynamic seismic test of a woodframe house. Dr Filiatrault is the author of a book and has authored over 50 journal papers. He received the 2002 Leon S. Moisseiff Award for his paper presented on the ASCE Journal of Structural Engineering titled "Cyclic Analysis of Wood Shear Walls."Richard Sause is a Professor of Structural Engineering and Director of the Advanced Technology for Large Structural Systems (ATLSS) Center at Lehigh University. He earned his Ph.D. (1989) and M.S. (1983) degrees in Civil Engineering from the University of California at Berkeley and his BS (1981) degree from Rensselaer Polytechnic Institute, and also spent several years in engineering practice. Dr. Sause’s research areas include earthquake engineering of concrete and steel-concrete composite structures, and structural applications of advanced materials. He has been active in earthquake engineering of precast/prestressed structures since 1993 through the PRESSS program funded by NSF and PCI, and was Co-Principal Investigator on 3 PRESSS projects at Lehigh and Principal Investigator of an NSF-funded study of precast diaphragm failures in the 1994 Northridge Earthquake. Dr. Sause is co-author of more than 100 journal articles and conference proceedings papers. He has given numerous research presentations at the PCI annual convention, and is a member of PCI’s ATLSS/PRESSS Committee.

VII. Budget and OrganizationThe primary research activity for which PCI funds are being requested is the LU experimental program. PCI funds will also be used for conducting parallel numerical simulations at UA and UCSD. This is reflected in the itemized budget for this proposal (See Appendix B). However, the activities described in the text of this proposal are contingent on both PCI funding and NSF matching and thus these ideas are expanded below.The team estimates that the scope of the research proposed here can be performed for approximately $400K (not including overhead) with the following breakdown: $200K LU, $100K UCSD, $100K UA. Typical university overheads (50-60%) have been reduced in the attached budget (UA – 25%; LU – 12%). However, further measures will be pursued if the proposal is funded including mechanisms for in-kind funds generated by UA to offset overhead (estimated recovery at 10-15%) and rules in place at UCSD pertaining to Industry Gifts (reduction to 4% overhead as was done in the PRESSS Program). Furthermore, the matching funds declared for the NSF GOALI program will significantly exceed the $200K PCI base funds: Additional match triggers include the donations of the producer members (estimated conservatively at $30K), the UA in-kind funds (estimated at $10-15K), the overhead relief being provided by LU (~$40K), and a substantial portion of the $30K PCI annually funds the ATLSS Center used for this activity. The team therefore envisions a matching fund trigger in the GOALI proposal in excess of $300K. The total amount of the PCI grant, in conjunction with a successful 1:1 GOALI match, will meet the resource requirements. It should be noted that this outcome is a product of both the reduced overhead levels and significant leveraging of resources at the consortium institutions. For example, UCSD is committed at fully funding a doctoral student to conduct the shake-table experimental work.Finally, the nature of the collaboration is such that UA emerged as the logical choice for lead institution among the group. However, the team will consider other arrangements if factors related to budget, scope of work or NSF matching mechanisms dictate. The team is actively exploring GOALI/NSF and overhead rate mechanisms, and will work closely with PCI to actively pursue all options to ensure the industry’s wishes are accommodated.

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