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Villanova University Dept. of Civil & Environmental Engineering CEE 4606 - Capstone II Structural Engineering 1 CEE 4606 - Capstone II Structural Engineering.

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Presentation on theme: "Villanova University Dept. of Civil & Environmental Engineering CEE 4606 - Capstone II Structural Engineering 1 CEE 4606 - Capstone II Structural Engineering."— Presentation transcript:

1 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 1 CEE Capstone II Structural Engineering Lecture 5 – Gravity Load Design (Part 1)

2 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 2 Outline 1.Review of Progress Report #1 Presentations 2.IBC Concrete Design Requirements 3.Beam & One Way Slab Design 4.Slab Thickness Considerations 5.Load Path and Framing Possibilities 6.Connection & Analysis Issues 7.Seismic Detailing Requirements 8.Work Tasks

3 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 3 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!!!

4 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 4 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 psi steel yield strength

5 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 5 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

6 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 6 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 – Seismic Design Requirements –Sec – Anchorage to Concrete Get to know this document!!!

7 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 7 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?

8 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 8 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

9 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 9 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

10 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 10 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    

11 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 11 Design Moments (Uniform Dist. Loading) Simple Spans –wL 2 /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

12 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 12 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

13 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 13 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

14 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 14 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

15 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 15 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!!!

16 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 16 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…

17 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 17 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…

18 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 18 L n = 10.5 ft. L n = 12.0 ft. L n = 14.5 ft. L n = 27.0 ft. Think we’ll need some additional framing members??? Note: columns automatically placed at each wall end or corner

19 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 19 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

20 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 20 Framing Concepts We can first assume that we’ll have major girders running in one direction in our one-way system Plan

21 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 21 Framing Concepts If we span between girders with our slab, then we have a load path, but if the spans are too long… Plan

22 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 22 Framing Concepts We will need to shorten up the span with additional beams Plan

23 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 23 Framing Concepts But we need to support the load from these new beams, so we will need additional supporting members Plan

24 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 24 Framing Concepts Now we have a viable plan… Let’s think back through our load path now to identify our “heirarchy” of members Plan

25 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 25 Framing Concepts One-Way Slab (continuous) Beams –Interior (T-beams) –Exterior (L-beams) Girders –Interior (T-beams) –Exterior (L-beams) Plan

26 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 26 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

27 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 27 Framing Concepts Now let’s go back through with a slightly different load path Plan

28 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 28 Framing Concepts We again assume that we’ll have major girders running in one direction in our one-way system Plan

29 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 29 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

30 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 30 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

31 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 31 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

32 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 32 Two Load Path Options

33 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 33 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)

34 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 34 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

35 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 35 Connection / Analysis Issues Let’s first consider our continuous one-way slab (12” strip shown) framing into an exterior (spandrel) beam Plan

36 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 36 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)

37 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 37 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

38 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 38 Connection / Analysis Issues Now let’s consider our beam-girder joints Plan

39 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 39 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)

40 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 40 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

41 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 41 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)

42 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 42 Connection / Analysis Issues Finally, let’s look at beam-column and girder-column joints Three situations: –Interior column –Exterior column –Corner column Plan

43 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 43 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

44 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 44 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

45 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 45 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

46 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 46 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)

47 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 47 Seismic Detailing Requirements for Reinforced Concrete - Introduction IBC Section 1910 ACI 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

48 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 48 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

49 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 49 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!

50 Villanova University Dept. of Civil & Environmental Engineering CEE Capstone II Structural Engineering 50 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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