CEE 4606 - Capstone II Structural Engineering

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Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

Capstone II

Structural Engineering

1

CEE 4606
-

Capstone II

Structural Engineering

Lecture 5


Gravity Load
Design (Part 1)

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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!!!

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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 53400 psi steel yield strength

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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. 1910


Seismic Design Requirements


Sec. 1912


Anchorage to Concrete


Get to know this document!!!

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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?

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

d

d

M

M

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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


Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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. 9.5.2.1

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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!!!

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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…


Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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…

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

Capstone II

Structural Engineering

22

Framing Concepts


We will need to
shorten up the
span with
additional beams

Plan

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

Capstone II

Structural Engineering

27

Framing Concepts


Now let’s go
back through
with a slightly
different load
path

Plan

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

Capstone II

Structural Engineering

32

Two Load Path Options

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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)

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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)


Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

Capstone II

Structural Engineering

38

Connection / Analysis Issues


Now let’s consider
our beam
-
girder
joints

Plan

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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)


Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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)

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

M
2

M
1

M

cl

M

cu

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

M
1

M

cl

M

cu

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

M
1

M

cl

M

cu

Plan

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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)

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

Capstone II

Structural Engineering

47

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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!

Villanova University

Dept. of Civil & Environmental Engineering

CEE 4606
-

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)