2008 NASCC JG Frames Presentation 10Jan08

8/11/2019 2008 NASCC JG Frames Presentation 10Jan08

1/48

1

Design of Lateral Load Resisting Frames

Using Steel Joists and Joist Girders

Presentation by:

James M. Fisher, Ph. D., P. E.

Vice President

Computerized Structural Design

Milwaukee, WI

Authored by

James M. Fisher, Ph.D., P.E.

Perry S. Green, Ph.D.

Joseph J. Pote, P.E.


2/48

2

Technical Digest 11


3/48

3

Technical Digest No. 11

The purpose of TD No. 11 is to present

information to the EOR, and the joist

manufacturer, for the design of single

story moment resisting joist and Joist

Girder frames.

Design considerations for both wind and

seismic lateral loads are presented.


4/48

4


The digest has been limited to single storyframes, not because of wind requirements,but because of current requirements for

seismic design; in particular, the use ofstrong beam, weak column systems whichare typically necessary when using trussconstruction in lieu of beams and girders.


5/48

5


The Digest illustrates procedures to:

Analyze,

Design, and

Specify joist and Joist Girder moment frames to resist

wind and seismic lateral loads.

The reader is assumed to be familiar with:

2005 AISC Specification for Structural Steel Buildings 2005 AISC Seismic Provisions for Structural Steel

Buildings

ASCE 7-05


6/48

6


Designing joist and Joist Girder structures as rigid

frames is no more difficult than designing rigid

frames with wide flange beams and columns.

To obtain a cost effective design the engineer must

be aware of the inter-relationships between framing

elements, i.e. joists, Joist Girders, columns, bracing

members and connections.

In general, the most economical design is one

which minimizes manufacturing and erection costs,

and one which reduces the special requirements

(seat stiffeners, chord reinforcing, etc.) for the

joists, Joist Girders and columns.


7/487

Design Methodology

The first consideration relative to the design of

the structure is to determine if rigid frame action

is required.

For single story structures the optimum framingsystem generally consists of braced frames in

both directions, and the use of a roof diaphragm

system to transfer wind and seismic loads to the

vertical bracing elements.


8/488

Design Methodology

The specifying professional and the joistmanufacturer must communicate design data andinformation to each other.

The specifying professional must specify thenecessary loading and stiffness data to the joistmanufacturer.

The specifying professional must indicate thetype of joist to column connections so that the

joist manufacturer can provide the joists with thegeometry that meets the design intent.

Dialog must occur between all involved partiesprior to final pricing and design.


9/489

Design Methodology

The joist manufacturer must design

the joists in conformance with the SJI

Specifications and other contract

requirements specified by the

specifying professional.


10/4810

Analysis Requirements

Forces and moments in single story joist rigid

frames are determined in a manner similar to

other Ordinary Moment Frames (OMF).

The first step is to perform a preliminary analysis.

In general, it is suggested that the OMF be

considered as a pinned based frame to eliminate

moment resisting foundations; however, for drift

control partially restrained or fixed bases can beconsidered.


11/4811

Analysis Requirements

After selecting trial member sizes for the columnsand joists, a computer analysis is performed todetermine forces, moments, and deflections (both

first-order and second-order) for the loadcombinations prescribed by the ApplicableBuilding Code.

Because a second-order analysis is a non-linearproblem, the analysis must be performed for each

required load combination.


12/4812

Frame Model

Model for IBC or ASCE Load Combinations


13/48

13

Analysis

Trial joist stiffness can be obtained from the SJIequations for the approximate moment of inertiafor a joist or a Joist Girder. The SJI equation for a

Joist Girder equals 0.018NPLd (LRFD),and 0.027NPLd (ASD)

where:

N = number of panel points

P = panel point load (kips) at factored load levelfor LRFD, and at nominal load level for ASD

L = girder length (ft.)

d = girder depth (inches)


14/48

14

Analysis

The SJI equation for the approximate

moment of inertia for a joist equals

26.767(WLL)(L3

)(10-6

) for both LRFD and ASD.where:

WLL= The RED figure in the K-, LH-, and

DLH-Series Load Tables

L = (Span

0.33) in feet for K-Series joists

L = (Clear span + 0.67) in feet for LH- and

DLH-Series joists


15/48

15

Analysis

Angle Size Unbraced Leng th

feet

Area

in.2

L = 4 L = 5 L = 6 L = 7

2L6 x 6 x 1 939 911 879 842 22.0

2L6 x 6 x 7/8 828 809 781 749 19.5

2L6 x 6 x 3/4 705 698 678 650 16.9

2L2.5 x 2.5 x 3/16 49 48 41 34 1.80


16/48

16

Frame Model

Model for AISC-Strong Beam, Weak Column


17/48

17

OMF Analysis


18/48

18

Pseudo Columns


19/48

19

Typical Connections


20/48

20

Basic Connection


21/48

21

Eccentricity Effect


22/48

22

Added Reinforcing


23/48

23

End Plate Type Connection


24/48

24

Plate Connection-Sidewall


25/48

25

Plate Connection-Interior


26/48

26

Specification of RequiredForces and Moments

IBC LRFD load combinations are used.

Nominal loads:

D = 15 psf L = 20 psf (reducible)

S = 5 psf

W (uplift gross) = 27.25 psf (windward roof)

= 17.3 psf (leeward roof)


27/48

27


Seismic Criteria:

R = 3.5 for OMF

SDS= 0.9297g

SD1= 0.39g r= 1.0

QE= 49 kips

Imin

= 6790 in.4for the exterior girders and 4570 in.4for the interior girder (analysis requirements).

Minimum width of top chord = 7.0 in. (weldrequirements).


28/48

28

Minimum thickness of bottom chord = 3/8 in.(weld requirements).

All top chord axial loads and end moments aretransmitted directly into the columns via the tieplates. No horizontal forces are transferredthrough the girder seats.

Chord splices must conform to the requirementsof the 2005 AISC Seismic Provisions, Section7.3a.

Controlling IBC Load Combinations are givenbelow for Joist Girder Mark Numbers G1 and G2,respectively:



29/48

29

Controlling IBC LoadCombinations

Mark G1

LRFD

Load Combination:

Panel

Load

(kips)

Left End

Moment

(kip-ft.)

Right End

Moment

(kip-ft.)

TC

Force

(kips)

BC

Force

(kips)

Remarks

1.4D + 1.4C

1.2D + 1.2C + 1.6(Lror S)

1.2D + 1.2C + 1.6W +

0.5(Lror S)

1.2D + 1.2C + 1.0E +0.2S

(1.2 + 0.2SDS) (D+C) +

QE + 0.2S

0.9D + 1.6W

+

+

+


30/48

30

Main Wind Force ResistingPressure Table

2005


31/48

31

2005 AISC Seism ic Prov is ionsSection 5.1

Designation of the seism ic load resis t ing system(SLRS)

Designation of the members and connections that

are a part of the SLRS Configuration of the connections

Connection material specifications and sizes

Locations of demand cr i t ical welds

Locations and dimensionsofpro tected zones Welding requirements as specified in Appendix W,

Section W2.1


32/48


33/48

33

Bracing


34/48

34

Examples 1 and 2


35/48

35

Examples 1 and 2


36/48

36

Example 1

The building is located in Charleston,

South Carolina. The building code to be

used is 2006 International Building Code

(IBC 2006).

The precast concrete shear walls at the

north and south ends of the building are

non-load bearing shear walls, and areused to resist the forces between the first

interior rigid frame and the end wall.


37/48

37

Example 1

Loading requirements are specified as:

Roof Loads:

Dead Load:1 psf Membrane

2 psf Deck

2 psf Insulation

3 psf Joists and Bridging

2 psf Girder

10 psf Total


38/48

38

Example 1

Collateral Load:

3 psf Sprinkler

2 psf Mechanical & Lighting

5 psf TotalLive Load:

20 psf Reducible per Code

(12 psf on Joist Girders)

Ground Snow Load = 5 psf

Roof Snow Load = 5 psf (ASCE 7, Section 7.3,low slope roof criteria)


39/48

39

Example 2

Wind Load = 120 MPH Exposure C

Seismic Load: Charleston, South Carolina

Serviceability Requirement: Maximum drift = H/100 (10 year wind)


40/48

40

Examples 1 and 2 Comparison

Example 1: Charleston, SC

Wind Base Shear (120 mph) 22.9 kips per frame line (Factored by 1.6)

Seismic Base Shear (R=3.5) 49.0 kips per frame line

Example 2: Jackson, MS

Wind Base Shear (120 mph) 22.9 kips per frame line (Factored by 1.6)

Seismic Base Shear (R=3.0) 14.3 kips per frame line


41/48

41

Example 1: Exterior Columns


42/48

42

Example 1: Interior Columns


43/48

43

Example 2: Exterior Columns


44/48

44

Example 2: Interior Columns


45/48

45

Example 1 (120 mph, SDC D) Columns: Exterior W18x86, Interior W18x97

Total Column Weight = 12,200 lbs

Girder Weight = 6,300 lbs Total Weight = 18,500 lbs per bay

Example 2 (120 mph, SDC B) Columns: Exterior W21x111, Interior HSS 8x8x3/16

Total Column Weight = 8700 lbs Girder Weight = 3200 lbs

Total Weight = 11,900 lbs per bay

Examples 1 and 2 Comparison


46/48

46

Appendix A

Appendix A contains a complete design of

the Joist Girders for Example 1


47/48

47

Acknowledgement

The authors of Technical Digest 11 wouldlike to thank: The Engineering Practice Committee and the

Research Committee of the Steel Joist Institute fortheir review and contributions to the writing of thisdocument.

John A. Rolfes, S.E., P.E. Vice President ofComputerized Structural Design for his assistance

in the preparation of the digest, and James O.Malley, S.E. Senior Principal,

DegenkolbEngineers, for his insightful review of the digest.


48/48

Thank you

2008 NASCC JG Frames Presentation 10Jan08

Documents

Transcript of 2008 NASCC JG Frames Presentation 10Jan08