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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
CEE 4606 - Capstone IIStructural Engineering
Lecture 5 – Gravity Load Design (Part 1)
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Outline
1. Review of Progress Report #1 Presentations
2. IBC Concrete Design Requirements3. Beam & One Way Slab Design4. Slab Thickness Considerations5. Load Path and Framing Possibilities6. Connection & Analysis Issues7. Seismic Detailing Requirements8. Work Tasks
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Progress Report #1 Comments
• Overall, a very good job• Comments on presentations:
– Timing good– Don’t worry about the intro stuff next
time– Know where our site is located – you
have coordinates that are accurate to within 3 miles!!!
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Progress Report #1 Comments
• Range of values:– 100 to 150 mph design wind speed– Seismic Design Category D
(unanimous)– 2000 to 2800 psi concrete strength– 49000 to 53400 psi steel yield
strength
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
IBC Concrete Design Requirements
• IBC Chapter 19• Mimics ACI 318 Code
– IBC 2000 version based on 1999 ACI 318– IBC 2003 will use 2002 version of ACI
318
• First seven sections (1901 – 1907) correspond to ACI 318 Chapters 1 to 7
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
IBC Concrete Design Requirements
• Section 1908 gives specific modifications to ACI 318– Deals with “meat” of ACI Code
• Sections 1909 – 1916 deal with specialized areas– Sec. 1910 – Seismic Design
Requirements– Sec. 1912 – Anchorage to Concrete
• Get to know this document!!!
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Load Path / Framing Issues
• Building Frame System– Frame for gravity load– Shear walls for lateral load
• Consider support of the chapel gravity loads:– Where do the columns go?– What beams do I need?– How do I design my slab?
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Beam & One Way Slab Design Review
• We presumably know how to do the following from CEE 3422:– Design a rectangular beam of
unknown cross-section size– Design a rectangular beam of known
cross-section size– Design a simply supported one way
slab
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Beam & One Way Slab Design Review
• We presumably know how to do the following from CEE 3422:– Design a T-beam for positive moment– Design a T-beam for negative moment– Design a doubly reinforced beam
(beam with compression reinforcement)
– Design a beam for shear
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Design of Continuous Beams and Slabs
• You know how to design cross-sections for positive or negative moment
• Reinforcement follows the moment diagram
• Why continuous spans?– Moments – Deflections
Two Simple Spans
Continuous over Center Support
Gap
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Design Moments (Uniform Dist. Loading)
• Simple Spans– wL2/8
• Continuous Spans– Analysis far more complicated– What type of fixity do we actually have?– Must consider effects of patterned
loading– Formation of plastic hinges allows for
moment redistribution
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Design Moments – Continuous Spans
• We have four analysis options– Elastic Analysis (preferably STAAD)– Elastic Analysis w/ Moment
Redistribution– Approximate Frame Analysis– ACI Approximate Moment Coefficients
• See McCormac text Chapter 13
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Slab Thickness Considerations
• What governs the thickness of a slab?– Flexural Strength– Shear– Deflections
• Usually, deflections will govern the thickness requirements for a one-way slab– Size slab based on deflection requirements– Check shear– Design reinforcement for flexure
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Slab Thickness Considerations
• Review McCormac text, Ch. 5 (serviceability) and Ch. 3 (one-way slabs)
• Review notes from CEE 3422, lectures on one-way slab design and serviceability
• ACI Sec. 9.5.2.1
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Slab Thickness Considerations(such that we do not need to compute
deflections)• For simply-supported beams, total beam
depth ‘h’ must be at least L/16– A 16 ft. long simply supported beam must be
at least 12 in. deep.
• For simply-supported one-way slabs, total slab thickness ‘h’ must be at least L/20– A 10 ft. long simply supported one-way slab
must be at least 6 in. deep.
• You will have to look up other values!!!
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Slab Thickness Considerations
• Something to keep in mind….– Your material properties!– These tables are based on normal
strength concrete– You may wish to consider creative
ways to adjust tables for your low concrete strength• Hint: Think about what the key concrete
material property related to deflections is…
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Load Path / Framing Possibilities
• Now we can begin to develop a framing plan for our structure– Typical practice on site is a 5 in. thick slab– We have a methodology to determine how
far a slab of a given thickness can span– Do our material properties have any effect?
• Let’s look at a plan view of the two-story section…
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Ln = 10.5 ft.
Ln = 12.0 ft.
Ln = 14.5 ft.
Ln = 27.0 ft.
Think we’ll need some additional framing members???
Note: columns automatically placed at each wall end or corner
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Framing Concepts
• Let’s use a simple example for our discussion…
• Column spacing– 30 ft. on center
• Think about relating it to your design as we discuss…
Plan
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Framing Concepts
• We can first assume that we’ll have major girders running in one direction in our one-way system
Plan
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Framing Concepts
• If we span between girders with our slab, then we have a load path, but if the spans are too long…
Plan
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Framing Concepts
• We will need to shorten up the span with additional beams
Plan
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Framing Concepts
• But we need to support the load from these new beams, so we will need additional supporting members
Plan
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Framing Concepts
• Now we have a viable plan…
• Let’s think back through our load path now to identify our “heirarchy” of members
Plan
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Framing Concepts
• One-Way Slab (continuous)
• Beams– Interior (T-beams)– Exterior (L-beams)
• Girders– Interior (T-beams)– Exterior (L-beams)
Plan
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Framing Concepts
• Note that by running the one-way slab in this EW direction, we are actually making the EW running beams our major girders
• The NS running beams simply transfer the load out to these girders (or directly to a column) Plan
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Framing Concepts
• Now let’s go back through with a slightly different load path
Plan
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Framing Concepts
• We again assume that we’ll have major girders running in one direction in our one-way system
Plan
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Framing Concepts
• This time, let’s think about shortening up the slab span by running beams into our girders.
• Our one-way slab will transfer our load to the beams. Plan
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Framing Concepts
• With this approach, we have already established our “heirarchy”
• The only difference is in the “direction” of our load path– 90 degree rotation
Plan
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Framing Concepts - Conclusions
• Either load path will work• In this case, they are identical• With a rectangular bay (instead of a
square) bay, there will be a difference
• Tradeoff is usually in number of supporting members vs. span of supporting members
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Two Load Path Options
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Framing Concepts - Considerations
• For your structure:– Look for a “natural” load path– Identify which column lines are best
suited to having major framing members (i.e. girders)
– Assume walls are not there for structural support, but consider that the may help you in construction (forming)
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Connection / Analysis Issues
• With continuous reinforced concrete framing systems, connections are a major issue with respect to:– Detailing of reinforcement at these
congested areas– Assumptions regarding fixity of
beams and slabs
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Connection / Analysis Issues
• Let’s first consider our continuous one-way slab (12” strip shown) framing into an exterior (spandrel) beam
Plan
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Slab-Exterior Beam Connection
• Slab is a six span continuous system• Some fixity at end of slab due to torsional
rigidity of exterior beam, but what happens when beam and slab crack?– Do we want to count on fixity?
• Also, if we design slab for negative moment here, we must develop reinforcement (like a cantilever)
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Slab-Exterior Beam Connection
Typical assumptions:– Simple support
at end– No moment in
slab at end– Place some
reinforcement at top of slab to control cracking
– Design exterior beam for minimal torsion
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Connection / Analysis Issues
• Now let’s consider our beam-girder joints
Plan
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Beam-Girder Connection
• Beam is a two span continuous system• Similar situation: some fixity at end of beam
due to torsional rigidity of exterior girder, but what happens when beam and girder crack?– Do we want to count on fixity?
• Also, if we design beam for negative moment here, we must develop reinforcement (like a cantilever)
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Slab-Exterior Beam Connection
Typical assumptions:– Simple support at
end– No moment in
beam at end– Place some
reinforcement at top of beam to control cracking
– Design exterior girder for minimal torsion
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Analysis – One-Way Slab & T-Beams
• For the simple elements just described, where supports are provided by beams and girders,– Supporting elements have some stiffness,
but it is fairly small– Assumption of treating one-way slabs and T-
beams as continuous beams is valid– A frame analysis is not needed since there
are no columns involved– Simple analysis methods can be used if all
assumptions are met (i.e. ACI moment coefficients)
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Connection / Analysis Issues
• Finally, let’s look at beam-column and girder-column joints
• Three situations:– Interior column– Exterior column– Corner column
Plan
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Interior Column Connection
• Girders framing in to a column:– Columns will provide some rigidity – Moments will depend upon
distribution of stiffness– Frame analysis is warranted to
determine these moments– Unbalanced loading (patterned
live load) must be considered– Goal: Determine moments in
girders (they will not necessarily be equal), as well as axial load & moment combinations for columns
• Beam/girder reinforcement must be continuous through joint
Plan
cl
cu
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Exterior Column Connection
• Same basic situation:– Columns will provide some rigidity – Moments will depend upon
distribution of stiffness– Frame analysis is warranted to
determine these moments– Unbalanced loading (patterned live
load) must be considered– Goal: Determine moments in
girders (they will not necessarily be equal), as well as axial load & moment combinations for columns
• Beam/girder reinforcement must be developed for negative moment
Plan
cl
cu
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Corner Column Connection
• This is essentially the same situation as an exterior column
• Note that where we have beams (not girders) framing into columns, the same principles apply– However, these moments are
typically very small and will usually not control the design
cl
cu
Plan
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Analysis – Girders & Beams Framing Into Columns
• For these elements, support is provided by columns
• Columns have substantial stiffness and will attract some moments– Assumption of treating these girders and
beams as continuous beams is not valid– A frame analysis is needed to determine the
appropriate distribution of moments– Elastic analysis is recommended (STAAD,
PCABeam)
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Seismic Detailing Requirements for Reinforced Concrete - Introduction
• IBC Section 1910• ACI 318-99 Chapter 21• These two sections, together,
identify specific detailing requirements related to seismic design of concrete structures
• Level of detailing required is based on Seismic Design Category
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Work Tasks
• Determine final loads on the structure– Gravity loads (dead, live)– Lateral loads (seismic, wind)
• Truss analysis on roof & design of roof members
• Detailing of roof-to-structure connection• Develop a load path (framing plan) to
support the gravity loads associated with the second story chapel
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Work Tasks
• Look into how the selection of Seismic Design Category D will affect concrete design detailing requirements for your beams, columns, and slab
• Work on design of one-way slab, beams, and girders– We will discuss design for shear and torsion
next time!
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Villanova UniversityDept. of Civil & Environmental Engineering
CEE 4606 - Capstone IIStructural Engineering
Assignment for Tuesday
1. Submit a detailed sketch showing your framing plan (load path for gravity loads) for the second story chapel– Identify all columns, beam, and girder locations, and
specify a slab thickness
2. Summarize on one sheet how the selection of Seismic Design Category D will affect the detailing of your structure– Use a bullet item / list format to identify specific
detailing requirements for your beams, columns, and slab
– Don’t consider shear walls for now (they will be masonry)
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