Methodology for Detailing - Applied to Point-Supported-Glass Wall Systems

A Methodology for detailing - Applied to Point-Supported-Glass Wall Systems

by

Xiaojun Cheng

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A Thesis Presented to the FACULTY OF THE SCHOOL OF ARCHITECTURE

UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the

Requirements for the Degree MASTER OF BUILDING SCIENCE

May 2006

Copyright 2006 Xiaojun Cheng

Chapter II – Research Methodology 2.1 Statement Architectural detailing is primarily left to experience in professional practice rather than formal education. There are few publications discussing strategies of detailing with demonstrations using a specific type of structure. This thesis presents a methodology to teach architectural detailing illustrated and demonstrated on case studies of Point-Supported-Glass walls. 2.2 Hypothesis This thesis assumes a methodology can be developed to teach students and young architects architectural detailing. The methodology is based on rules and process, considering assembly, installation, tolerance, functionality and aesthetics using PSG walls as demonstrations. 2.3 Thesis structure and research process The methodology of this thesis is based on rules and process. The eight rules are: Know basic requirements of PSG wall systems Know design concept Know principles Study from good designers and good detail examples Consult with manufacturers as needed Create your own detail designs (process) Mock-up examples and test as needed On site supervision as needed

Among the eight rules, four are explained in details, which are: Know basic requirements of PSG wall systems Know principles Study from good designers and good detail examples Create your own detail designs (process)

Each of these four rules is explained in detail below: “Know basic knowledge of PSG wall systems” This introduces the basic knowledge of PSG wall systems, including: The materials generally used in PSG walls The components of a PSG wall

“Know principles” This introduces the principles which should be considered in detail design. This thesis discusses two types of principles, general principals and important principles. The general principles are normally more emphasized during macro scale design, which is not the focus of this thesis. The important principles are generally more emphasized during micro scale design, which is the focus of this thesis. The general principles and important principles are listed as below. The general principles are emphasized in macro scale design and they are not the focus of the thesis. Therefore the thesis only gives brief introduction for each one. They are: Function, structure type, structure behavior, material property, life cycle analysis

(LCA), maintenance, light control, thermal control, ventilation, cost control, sound control, water proof, aesthetics, integration, fire resistance, water proof, synergy

Then the paper selects six points from the principals listed above to give more description for each one. The reason for this is because the author considers these six points more critical to PSG walls than other points. The six points are: Light control Structure behavior Thermal control Sound control Cost control Integration

The important principles are generally more emphasized in micro design scale, and therefore they are described in detail. They are: Tolerance Manufacture, assembly and installation Water resistance Maintenance Aesthetics

“Study from good designers and good detail examples” The thesis recommends some representative PSG projects to readers. The projects are categorized into six groups based on the back up structure types, which are: Metal frame Truss Tension cable Cable net Glass fin Other types

“Create own detail designs (process)”

The thesis then introduces a process which can be a guide to follow to make a detail design. The process includes nine points. The thesis firstly introduces the nine points, one by one, and then used the four case studies to illustrate and support the nine points. In order to make the process easy to understand and follow, during the case studies, the thesis introduces a sequence for the nine points. This sequence, however, is only one of possible sequences. If choosing different sequence, the result might be different. But how to determine the sequence, and what is the effect, are not going to be discussed in the thesis. The nine points of the process are: Find out the infrastructure Determine modular size Determine the back up structure Make a checklist of all elements based on four categories

Category 1 – Infrastructure elements Category 2 – Glass wall elements Category 3 – Elements for openings Category 4 - Additional devices

Determine the position, shape and size of each element Find out all Connections based on eight categories

Category 1 – Connections within glass wall Category 2 – Connections within openings Category 3 – Connections within additional devices Category 4 – Connections between glass wall and additional devices Category 5 – Connections between glass wall and openings Category 6 – Connections between openings and additional devices Category 7 – Connections between glass wall and infrastructure Category 8 – Connections between openings and infrastructure Category 9 – Connections between additional devices and infrastructure

Determine the material and method for each connector Any other special requirements Detailing each connection

The first eight points are to make preparation for the ninth point, which is “detailing each connection.” For the ninth point, because different connections have different requirements and emphasis in detailing, it is advisable to provide a method for each typical connection type. Examples of connection types with different requirements are the connection between glass and infrastructure, the connection between glass support structure and infrastructure, the connection within the glass panels, and the connections within the glass support structure. Therefore, the thesis studies one typical connection for each of the first two case studies and develops a specific detailing method (shown as a process) for each typical connection. For instance, the detailing process for a typical connection between cables and struts (the elements involved in the support structure of a cable-supported glass wall), is shown as below:

Step 1 – Draw concentric center line connections Step 2 – Draw connector size as dotted line Step 3 – Define tolerance between connectors Step 4 – Explore connector options Step 5 – Design connecter Step 6 – Make adjustment (Such as reducing connector and checking eccentric stress

shown in the first case study) After exploring the rules and process, the thesis uses four PSG projects from ASI (Advanced Structures Incorporated) as demonstrations. The paper also makes a brief study of some projects with detail failures. Detailed research for projects with failures is left for future studies. The four case studies from ASI are: University of Connecticut, Stamford, Connecticut McCarren International Airport, Las Vegas UBS Building at One North Wacker Drive, Chicago, Illinois Ha-Lo, Niles, Illinois

Each of the four case studies represents a typical structural type of PSG wall system. They are cable truss, truss, cable net and glass-fin, respectively. For each project, a typical PSG wall section is used to illustrate and support the detailing process developed for the methodology. Then, for the first two case studies, a typical joint is selected to further describe the detailing process which is specifically used for a typical cable joint. To make the detailing process easy to follow, a flow chart is developed to explain each step visually. For instance, the following chart describes the detailing process of a typical cable joint in the first case study.

Fig. 2-1 The detailing process of a typical cable joint At the end of the thesis, a conclusion is drawn from the research, including: Feedback from peers and experts Suggestions for future studies Useful sources

2.4 Products The research results in two products. One product is the written thesis and the other one is a web-page of the methodology. The thesis provides the complete description of the research, including the hypothesis, research methods, and research results. The web-page is used as a teaching tool for students and young architects to study the detailing methodology.

Chapter VIII Case study one – University of Connecticut Student Center 8.1 Introduction

8.1.1 Project information Climate The latitude of Connecticut is 41.07N, and longitude is 073.25W. Connecticut has a generally temperate climate with warm summer and mild winter. The average temperature in January is 27°F (–3°C), and in July 70°F (21°C). The lowest recorded temperature is –32°F (–36°C) in Falls Village in Feb1943, and the highest is 106°F (41°C) in Danbury in July1995. The rainfall is evenly distributed throughout the year, with an annual rainfall 46.2in (117cm) from 1971 to 2000. (http://www.city-data.com/states/Connecticut-Climate.html) The following charts show the average temperature, humidity, sunshine, cloudy days, precipitation, and wind speed around the year in Stamford.

Fig. 8-1 Stamford climate data (http://www.city-data.com/city/Stamford-Connecticut.html)

General project information Location: Stamford, Connecticut Architects: Perlins Eastman Architects Associate architects: Dubose Associates Engineers: Cosentini Associates (mechanical); Purcell Associates (structural); Allan Davis Associates (civil) Consultants: Advanced Structures Inc. (structural glazing); Scott B. Page (program); Jack Curtis & Associates (landscape); Chermayeff & Geismar (graphics); Donegan & Associates (consulting architect); Ann Kale Associates (lighting) Sources: Uninsulated metal Panel: Alply Insulated metal Panel: Criterion Glass curtain wall: Pilkington Aluminum windows: Vistawall, Pilkington Insulated glass: Pilkington, Viracon Skylights: Architectural Skylight Glass entrance doors: Blumcraft Cherry veneer doors: Weyerhauser Lighting: Zumtobel, Bega Total Cost: $40 million Total area: 253,000 SQFT Unit cost: $158/SQFT Brief introduction Stamford campus building is located in downtown Stamford. It is the renovation of an old building of which only the structure and floor slab remaine, but the brick skin was removed and substituted by glass and concrete. The south part of the building is a library, and the north part consists of classrooms and offices. The south-facing and 440-foot long glass façade is one of the most impressive features of the building. It not only brings sufficient daylight into the academic concourse, but also makes the building close and

friendly to pedestrian, which strengthens the designers’ idea to bring the building “closer to the community it serves.” The whole glass façade is divided into two parts by a concrete slab. The lower part is about 11 feet, supported by regular mullion. The 36-foot glazing of the upper part is pointed fitted, and supported by cable (rod) truss. This part is what ASI developed. For this project, ASI was hired by Pilkington as a subcontractor to provide the design and detailing of the glass wall and support system. The glass panes and fittings were not the responsibility of ASI; in stead, they were designed by W&W Glass Systems, Inc., another subcontractor of Pilkington. (Langdon, P., 1998) The glass façade is the “nation's first Pilkington Planar glazing system supported by the longest, clear span, lenticular cable truss. The facade was made up of green-tinted, low-e coated, insulated glass panels supported by stainless steel, four-point castings.” The glass wall includes “several 900 corners supported by custom-designed corner trusses. The key feature of the support structure was the pretensioning methodology created to adequately support this unique clear span structure.” (http://www.wwglass.com/) 8.1.2 Images The following images are the site plan & first floor plan (Fig. 8-2), exploded axonometric (Fig. 8-3), exterior and interior photos (Fig. 8-4) of the building.

Left: Site plan 1. Stamford Campus Building 2. Parking garage 3. Franklin Plaza 4. C.L.”Whitey” Heist Park 5. Rippowam River 6. St. Andrew’s Church

Left: First floor plan 1. Entrance 2. Concourse 3. Library 4. Bookstore 5. Conference center entrance 6. Light spine 7. Auditorium 8. Classroom 9. Multiuse area 10. Mechanical

Fig. 8-2 Site plan (top) and first floor plan (bottom) of the building of the

University of Connecticut (Langdon, P., 1998)

Fig. 8-3 Exploded axonometric (Langdon, P., 1998)

(b) North facade

(Langdon, P., 1998) (a) South façade

(Langdon, P., 1998)

(c) Inside view looking from east to west

(Langdon, P., 1998) (d) South façade

(http://www.wwglass.com/)

(e) Inside view from north to south

(Langdon, P., 1998) (f) In side view looking from east to west

(http://www.wwglass.com/)

Fig. 8-4 Exterior and interior photos of the building of the University of Connecticut

Two detailing processes are introduced in this chapter, using case studies. Firstly, a typical wall section is used to explain the detailing process of a typical PSG wall (see Chapter 8.2). Secondly, a specific joint is selected to illustrate the detailing process of a typical joint of cable and strut (see Chapter 8.2.9). Fig. 8-1 shows the interior views, description, elevation and section of the glass wall used to illustrate the detailing process.

The 440 feet long and 35.4 feet high south glazing facade of the Student Center, University of Connecticut, features 5 feet wide and 5.83 feet high glass panes of double-glazing, green-tined and low-E coated glass. (http://www.wwglass.com/) The glazing is point-supported, and the fixing type is Pilkington Planer System. The glazing support attachments are stainless steel four-way spiders, attached to stainless steel double-curved tension rods. The glass wall is attached to horizontal infrastructure of two square-tube steel beams.

(a) Interior view (b) Description of the PSG wall based on five layers

6'Square steel tube

7'-2"

5'

5.83'

A typical joint used in Step 8 and Step 9 (see 8.2.8 & 8.2.9)

Strut pipe

Glass

Rods

Square steel tube

35.4'

(c) Interior view of the wall (d) Elevation (e) Section

Fig. 8-5 Interior views, description, elevation and section of the glass wall

(ASI, modified) 8.2 Detailing process for a typical section 8.2.1 Identify the infrastructure

(http://www.wwglass.com/) (ASI, modified) Infrastructure type – upper beam to lower beam (horizontal) Infrastructure material – steel frame (stiff)

In this example, the infrastructure consists of two horizontal beams (see the wide lines in the image left above). This means that the back up structure is a vertical structure. Here, vertical cable trusses are used. The materials of the beams are steel, which is generally strong, and can resist the cable tension,

Fig. 8-6 Case study #1 - Illustration and description of step 1 8.2.2 Determine modular size

(ASI, modified) (ASI, modified)

5’ × 5’ 10” based on glass pane limitation In this project, the modular size of the glass wall was determined by the size of glass pane, which is 5 feet width and 5’ 10” height.

Fig. 8-7 Case study #1 - Illustration and description of step 2 8.2.3 Identify the back up structure

(Drawn based on ASI drawings)

Primary structure – Vertical curved tension rods are used as the back up structure; Vertical straight

rods are used additionally; Horizontal strut pipes are compression members Secondary structure – Horizontal bracing rods are used to strengthen the structure;

Horizontal straight rods are used additionally Material – stainless steel rods; steel pipe

Fig. 8-8 Case study #1 - Illustration and description of step 3

8.2.4 Make a checklist of all of the elements based on four categories Category Elements

Two horizontal beams (like roof and ground) Top beam Bottom beam

Category 1 – infrastructure

Steel beam: TS 16×20 Steel grid: TS 16×14

Steel beam: TS 18×14 Steel rid: W 14×?

Category 2 – Glass wall

Glass panels

Glass fittings

Back up structure elements

elements Double glazing, green-tinted, low-E coated

Four way spider

Strut pipe

Truss rod

Vertical rod

Bracing rod

Horizontal rod

Category 3 – Elements for openings

N/A

Category 4 - Additional devices

N/A


(ASI, summarized) 8.2.5 Define the position, shape and size of each element

(ASI, modified)

Identify the size of the given infrastructure The size of glass panels is defined by architects and/or glass manufacturers. The size of glass fittings is determined by manufacturers and/or in consultation with architects. The size of strut pipe and rod are determined through calculation and experience.


The following gives out an example of how to determine the size of the key elements including strut pipe, truss rod, vertical rod, horizontal rod, and diagonal rod, through calculation.

The sizes ASI used for these key elements are as the following: Strut pipe: 2 3/8”Ф (Diameter) Truss rod: three different sizes were used: Typical truss rod 1/2” Truss rod at corner: 3/4” Truss rod next to gate: 5/8” Vertical rod: 3/8” Horizontal rod and diagonal rod: 1/4” (this number is estimated from the DWG drawing by ASI) The calculation in the following will show how ASI determined these sizes. The size of truss rod: We need to consider the following load: Gravity load – 10psf Gravity load includes dead load and live load. In this case, we only consider the dead load because there is no live load. Gravity load is critical for seismic load. The bigger the gravity load is, the higher the seismic load. Since glass wall is lightweight structure, in most cases, the seismic load can be ignored. Seismic load – 2 psf V=CsW Cs: 20% W: 10psf V = 20%×10psf = 2psf Wind load – 30 psf for typical locations; 45psf for corners Since the seismic load (2psf) is much smaller than the wind load (30psf), consider the wind load only. Thermal load – Temperature range: ±75oF Thermal stress ft = α ∆t E ft – Thermal stress α – Coefficient of thermal expansion ∆t – Temperature range E – Elastic modulus In this case, stainless steel rod is the bearing structure, so we need to consider the thermal stress of rod. The Coefficient of Thermal Expansion (α) of steel is 6.5 × 10-6 oF. The Elastic Modulus of steel is 29 × 106 psi. The temperature range is 75 oF. Therefore, the thermal stress of rod is: ft = α ∆t E = 6.5 × 10-6 oF × 75 oF × 29 × 106 psi = 14137 psi ≈ 14 ksi Tension of truss rod (the curved rods are also called truss rods): Truss rod space: 5’ Allowable truss rod load: 10,000 LBS Allowable rod stress: Fa = 50 ksi (high stress steel)

Wind load: 30 psf Truss rod length (L): 35’ Truss rod depth (D): 4.5’ Tributary area: 5’ Tributary load on each truss rod (uniform load): W = 30 psf × 5’ = 150 plf Global moment: M = WL2/8 = 150 plf × (35’) 2 / 8 = 22969 lbf Horizontal reaction: H = WL/2 = 150 plf × 35’ / 2 = 2625 # Vertical reaction: V = M/D = 22969 lbf / 4.5’ = 5104 # Tension: T = (V2 + H2) ½= (26252 + 51042) ½= 5739 # Metallic cross section required: Am = T/Fa = 5739 / 50 ksi = 0.115 in2

Gross cross section (70% metallic) Ag = Am/0.70 = 0.115 / 0.70 = 0.164 in2 Rod size Ф = 2(Ag/π) ½ = 2 (0.164 / 3.14) ½ = 0.456 in Use Ф = ½ inch, therefore the cross area is: A = π (Ф/2)2 = 3.14 × (0.5/2) 2 = 0.196 in2 Ultimate stress of rod: US = T/A = 5739 / 0.196 = 29281 ≈ 30 ksi Pre-stress of rod: PS = ½ US = 15 ksi Thermal stress is 14 ksi In winter, rod shrinks, causing bigger tension Stress is 15ksi + 14kis = 29 ksi In summer, rod expands, causing smaller tension, Stress is 15ksi – 14ksi = 1ksi > 0, ok! Total maximum stress of rod: f = ½ US + PS + TS = 15ksi + 15ksi + 14ksi = 44ksi < 50 ksi, ok! Size of strut pipe: Wind load: 30 psf Strut length: 5’ Tributary area: 5’ × 5.8’ = 29 f2 Tributary load on each strut: W = 30 psf × 29 f2 = 870 #, check <Manual of Steel Construction>

Fig. 8-11 Case study #1 - Illustration and description of step 5 – Example of structural calculations (Instructed by G.G. Schierle, 2005)

8.2.6 Define Connections based on eight categories

(ASI, modified)

Category 1– Connections within glass wall

Glass + Glass, Glass + Spider, Spider + Strut, Strut + Rod Category 2 – Connections within openings (Does not apply in this case) Category 3 – Connections within additional devices (Does not apply in this case) Category 4 – Connections between glass wall and additional devices (Does not apply in this case) Category 5 – Connections between glass wall and openings (Does not apply in this case) Category 6 – Connections between openings and additional devices (Does not apply in this case) Category 7 – Connections between glass wall and infrastructure

Glass + Ground, Glass + Roof, Rod + Ground, Rod + Roof Category 8 – Connections between openings and infrastructure (Does not apply in this case) Category 9 – Connections between additional devices and infrastructure (Does not apply)


8.2.7 Determine the material and method for each connectors From step 6, we can see that there are eight connections. They are: Glass + Glass, Glass + Spider, Glass + Strut, Strut + Rod, Glass + Ground, Glass + Roof, Rod + Ground, and Rod + Roof.

Glass + Glass – structural silicone The left image show the typical detail of double glazing insulating glass joint. (Left image comes from http://sweets.construction.com/)

Glass + Spider – bolted together Using standard Pilkington Planar System, we can get perfect smooth exterior surface. The connection detail of Glass + Spider is usually from the manufacturer who provides the spider. (Above left image is edited base on ASI drawings. Below left image comes from http://www.wwglass.com/)

Strut pipe

Weldings

Bolt holeGlass

Steel spider

Glass fixing(Pilkington Planer)

Threaded bolt

Solid bar

This step is to define the material and method for connectors. In this case, glass panes are fixed to the four-way spider by standard Pilkington Planer system, which creates a flush exterior surface. The spider is connected to the strut pipe by a solid bar. The spider is bolted into the solid bar, and the solid bar is welded to the strut pipe. The threaded bolt was provided by the glass manufacturer who provided glass and fixings, but the size of the bolt was dependent on the diameter of the bolt hole, which was defined by ASI. The size of the bolt (5/8” diameter, 2”deep) was defined to assure structural safety.

Strut + Rod – connected by a steel plate; the plate is welded to the strut; the rod is bolted to the plate. (image from ASI, modified)

Glass + Ground

Glass + Roof – A steel pocket holds the glass pane; the pocket is bolted to a steel angle; the angle then is welded to the infrastructure. Please notice that, the pocket should have enough height so that the glass can move vertically freely under any vertical load (such as seismic), or thermal expansion. (image from ASI, modified)

Rod + Ground (steel tube) – connected by a plate and an anchor plate; the anchor plate is welded to the steel tube; the plate is welded to the anchor plate; the rods are bolted to the plate

Rod + Roof (steel tube) – connected by a plate and an anchor plate; the anchor plate is welded to the steel tube; the plate is welded to the anchor plate; the rods are bolted to the plate (image from ASI, modified)


(Drawn based on ASI drawings) 8.2.8 Any other special requirements

Gusset plate (connector)

Force applied during installaion

Hole for pre-stressing

This step is to define special requirement for manufacture, assembly and installation, as well as any other requirements that are not covered in other steps. For example, a hole is designed in the gusset plate for pre-stressing purpose. Because the steel rods are tension members, prestress is needed to avoid compressive stress under any load (compressive stress would buckle the rods and cause instability).

Fig. 8-14 Case study #1 - Illustration and description of Step 8

8.2.9 Detailing each connection A typical joint type (cable + strut) shown in Fig. 8-14 is used to illustrate the detailing process of a specific connection. Please notice that this joint is eccentric. However, when starting to detail, concentric connection should always be considered first (Fig. 8-15). The reason is that eccentric connection may cause bending stress in the joint. One should make concentric connections at first, and adjust it to eccentric connection only if needed. If eccentric connections are used, designers must check the resulting stress to ensure structural safety. The illustration of the steps will start with a concentric connection and then introduce the reasons for eccentric connection (Fig. 8-16 & Fig. 8-17). Then a detailing process starting with an eccentric connection is introduced (Fig. 8-18 & Fig. 8-19).

(b) Eccentric connection(a) Joint of cable + strut

Rod

Socket (Coupler)

Gusset plate(Connector)

Strut

(c) Concentric connection

Fig. 8-15 Case study #1 - Illustration and description of Step 9 - Eccentric and concentric conditions of the joint (Drawn based on ASI drawings)

The process to detail the joint starting from a concentric connection is: Step 1 – Draw concentric center line connections Step 2 – Draw connector size as dotted line Step 3 – Define tolerance between connectors Step 4 – Explore connector options Step 5 – Design connector Step 6 – Make adjustment (reduce connector and check eccentric stress)

These six steps are further explained in the flow chart below (Fig. 8-16). Each image in Fig. 8-16 is described in Fig. 8-17 (Image numbers of Fig. 8-16 correspond to respective numbers in Fig. 8-17).

4 4.1

6 6.1

5

4.1.1

Alternate connector options

3

2

4.2

4.3

1

4.2.1 4.2.2

4.3.1 4.3.2

Fig. 8-16 Case study #1 - Illustration and description of Step 9 - Flow chart of the detailing process starting from concentric connection (Drawn based on ASI drawings) Enlarged diagrams shown in Fig. 8-16

Image 1

Principles applied: Structural behavior (concentric connection) Always consider a concentric connection at first and adjust it to eccentric connection only if needed. Concentric connection requires that the center lines for all connected elements join at one point. Five center lines are drawn, four rods and one strut. Image 2

Principles applied: Manufacture & structure (size of available cable fittings A1) Structure (size of strut A2) Draw the size for the elements to be connected by dotted line. Here, the size of the strut (A2) and the size of sockets (A1) are needed. (Sockets connect strands or rods to other elements). A1 is provided by the strand manufacturer. A2 is defined by structural design, based on stress, material strength, and structural length of the strut (see image below). A2 may be also defined by needs to make connections. In this case A1 ≈ 1 1/2”, A2 = 2 3/8”.

Image 3 Principles applied: Tolerance (tolerance between adjacent sockets) Draw the tolerance needed between adjacent elements. Here, tolerances needed for the top rods (B1), and the bottom rods (B2) are B1 = B2 = 0.5” (reference). After drawing B1 and B2, one can see that the distances between the rods and the strut (B3 and B4), are obviously bigger than 0.5”, which is ok for the necessary tolerance.

Fig. 8-17 (continued) Image 4

Principles applied: Manufacture (socket dimensions) Structure (minimum socket size C2) Draw sockets connecting rods to strut. Firstly, get C1 and C2 from socket manufacturer (see image below) based on rod size. In this case C1 = 1 1/4", C2 ≈25/32”.

Image 4.1 Principles applied: Tolerance (between socket and gusset plate ) Aesthetics (connector shape) An egg-shaped gusset plate (connector) is designed to start. Note, tolerance (C3) is needed between the socket and gusset plate (see image above). C3 = 1/2" (reference). Considering the tolerance, the maximum gusset plate is defined. Image 4.1.1

Principles applied: Structure (pre-stressing to keep strands always in tension; minimum C5 to assure enough strength to resist shear force when applying prestress) Installation (a hole to pull down the connector for pre-stressing; diameter of the hole; enough space C4 for convenience of installation ) A hole is designed to apply pre-stress in strands. Enough space (C4) is needed for installation purpose. The hole diameter (Ø1) and C5 are defined based on the prestress force applied. The prestress force is defined by structural calculations. Image 4.2 – 4.3.2 are a few examples of connector alternatives.

Fig. 8-17 (continued) Image 5

Principles applied: Aesthetics (smooth curved edge of connector) Installation (larger space around the hole) Structure (sufficient weld length) For aesthetical reasons, the connector edge is curved. The strut ending (D1) is based on aesthetics and weld length required. The minimum strut ending D1 = 0”. (See images below). At this stage, the joint design is almost complete. However, there are still two items that could be improved: the connector looks a bit too bulky and the space around the pre-stressing hole looks too small.

Image 6 Principles applied: Aesthetics (reducing connector size) Installation (increase space around prestress hole) Structure (check eccentric stress) An eccentric connection can solve these problems (see dotted lines). By separating the center lines, the strand sockets may be placed closer to the strut to reduce the joint; and the space around the prestress hole can be increased for easier installation.

Image 6.1 Principles applied: Aesthetics (connector shape) Structure (allowing structural movement) An eccentric connection is designed to reduce the gusset plate and joint detail. However the eccentric joint may cause secondary stress in the strut. Thus, the strut must be designed to resist the eccentric stress in addition to any axial stress. Note, the concave shape of the gusset plate is partly because of aesthetics and partly because of functions (allowing the rods to rotate under structural movement).

Fig. 8-17 (Continued)

Fig. 8-17 Case study #1 - Illustration and description of Step 9 – Illustration of each image shown in Fig. 8-16 (Drawn based on ASI drawings)

Fig. 8-16 and Fig. 8-17 illustrate why the concentric connection is adjusted to an eccentric connection due to the size of fittings. Fig. 8-18 shows how the detailing process works for an eccentric connection. Each image shown in Fig. 8-18 is further illustrated in Fig. 8-19.

Alternate connector options

Step 1 – Draw eccentric center line connections Step 2 – Draw connector size as dotted line Step 3 – Define tolerance between connectors Step 4 – Explore connector options Step 5 – Design connector Step 6 – Make adjustment (the concave shape of the gusset plate to allow structural movement)

Fig. 8-18 Case study #1 - Illustration and description of Step 9 – Flow chart of the

detailing process starting from an eccentric connection (Drawn based on ASI drawings)

Enlarged diagrams shown in Fig. 8-18 Image 1

Principles applied: Structural behavior (concentric connection) Aesthetics (eccentric connection) As explained in Fig. 8-16 and Fig. 8-17, the concentric connection needs to be changed to an eccentric connection to fit the fiitings. The left image is the result of an eccentric connection, showing the five center lines of four rods and one strut. Because the eccentric joint may cause secondary stress in the strut, the strut must be designed to resist the eccentric stress in addition to axial stress. However, the principal of concentric connection is still favored Rod #1 & Rod #3 are connected to one point; as are Rod #2 & Rod #4 Image 2

Principles applied: Manufacture & structure (size of available cable fittings A1) Structure (size of strut A2) Draw the size for the elements to be connected by dotted line. Here, the size of the strut (A2) and the size of sockets (A1) are needed. (Sockets connect strands or rods to other elements). A1 is provided by the strand manufacturer. A2 is defined by structural design, based on stress, material strength, and structural length of the strut (see image 3). A2 may be also defined by needs to make connections. In this case A1 ≈ 1 1/2”, A2 = 2 3/8”.

Image 3 Principles applied: Tolerance (tolerance between adjacent sockets) Draw the tolerance needed between adjacent elements, the distance between the top two rods and the distance between the bottom two rods are bigger than 0.5”, which is needed for necessary tolerance. Here, tolerances needed are the distances between the rods and the strut, which are B1 = B2 = B3 = B4 = 0.5” (reference).

Fig. 8-19 (Continued) Image 3.1

Principles applied: Structure and aesthetics (check D1 and D2) After setting the B1 = B2 = B3 = B4 = 0.5” as shown in Image 3, it turns out that the distance between the restraining bolts in the top two rods and the strut (D1) is smaller than that of the bottom two rods and the strut (D2). (To determine D1 and D2, see Image 4. This is an example that the detailing process as shown in these images is not fixed. A designer should be able to adjust the process due to different circumstances.) Image 3.1.1

Principles applied: Structure and aesthetics (equal D1 to D2) To make the joint structurally balanced, D1 and D2 should be equal. Because D1 is smaller than D2, D1 is adjusted to be equal to D2 to ensure minimum clearance (tolerance) mentioned in Image 3. Another benefit to equal D1 to D2 is better aesthets The connector looks more balanced if D1 equals to D2.

Image 4 Principles applied: Manufacture (socket dimensions) Structure (minimum socket size C2) Draw sockets connecting rods to strut. Firstly, get C1 and C2 from socket manufacturer based on rod size (see Image 4 in Fig. 8-17). In this case C1 = 1 1/4", C2 ≈25/32”.

Fig. 8-19 (Continued) Image 4.1

Principles applied: Structure (pre-stressing to keep strands always in tension) Installation (a hole to pull down the connector for pre-stressing; diameter of the hole; enough space around the hole for convenience of installation ) A hole is designed to apply pre-stress in strands. Enough space around the hole is needed for installation purpose. The hole diameter (Ø1) and C3 are defined based on the pre-stress force applied. The pre-stress force is defined by structural calculations (typically half the ultimate stress). Image 3.2 – 3.4.3 are gusset plate alternates Image 5

Principles applied: Aesthetics (smooth curved edge of connector) For aesthetical reasons, the connector edge is curved. The strut ending (D1) is based on aesthetics and weld length required. The minimum strut ending D1 = 0”. (See Image 5 in Fig. 8-17). At this stage, the joint design is almost complete.

Image 6 Principles applied: Aesthetics (connector shape) Structure (allowing structural movement) The concave shape of the gusset plate is partly because of aesthetics and partly because of functions (allowing the rods to rotate under structural movement).


Fig. 8-19 Case study #1 - Illustration and description of Step 9 – Illustration of each image shown in Fig. 8-18 (Drawn based on ASI drawings)

Methodology for Detailing - Applied to Point-Supported-Glass Wall Systems

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