Needham & Associates

Needham & Associates

Consulting Engineers

Fort Wayne, IN
-

Overland Park, KS

http://www.needhamassoc.com

Serviceability Design of
Metal Buildings

•
Or….Why is my customer so
unhappy???

•
What does a contractor need to
know???

Your Speakers

•
Jeff Needham, Principal

–
P.E., S.E in 20 states, started firm in 1989 in
Fort Wayne

–
BS and MS from University of Kansas

•
Andy Carter, Principal

–
P.E., S.E in 25 states, started in PEMB in
1968

–
BS Virginia Military Institute, MS from
Georgia Tech

What Does Needham and
Associates Do?

•
General Practice Structural/Civil
Engineers

•
Consultants to PEMB Industry

–
Heavy Structures ( ex: large clear
-
spans,
steel mills, special structures)

–
Hardwall Buildings ( ex: site
-
cast, tilt
-
up
concrete)

Introduction

•
Why consider
serviceability
(source of
many problems and claims)

•
Owner input (must have active input,
common problem)

•
Specific to structure’s use

•
Easy to build in, difficult to repair


Example of Breakdown in
Serviceability Considerations

•
Probably lack of communication between
owner and contractor

•
Project in Terra Haute, IN


Flammable Vapor Build
-
up in
Insulation

Types of Serviceability Issues

•
Deflections and Drift (primary focus of this
talk)

•
Expansion/Contraction

•
Camber

•
Vibration

•
Corrosion

•
Connection Slip

Responsibility for Determining
Serviceability Requirements

•
Generally not code issue

•
Building manufacturer’s consideration only if
informed by dealer

•
Entity (Architect or Owner) specifying the
building parameters specifies criteria

•
Serviceability criteria need owner agreement
of requirements & cost


Basic Deflection and Drift Ratios

Wall Considerations
-

Drift

•
Metal walls usually have no real limit

•
Masonry/tilt
-
up/precast wall vs. frame drift

•
Base condition free to rotate
-

H/100

•
Base condition fixed to rotate
-

H/200

•
Do not use unreinforced masonry walls with
PEMB


Typical NEW PEMB Hardwall
Buildings

•
Designed for strict serviceability issues

•
Load bearing walls


Wall Considerations
-

Deflection

•
Wainscot walls & framing above

•
Total deflection

–
sum of frame drift & girt deflection

•
Spandrel Beam (single girt) L/240, but not
more than 1.5 inches

•
Details to enhance compatibility of
materials, allow for movements


Special Considerations for
Bridge Cranes

•
Complex topic

•
Common drift limit H(eave ht)/200 under
crane lateral load

•
Crane beam deflection L(bay)/600 for vertical
deflection

•
Crane beam deflection L(bay)/400 for
horizontal deflection


Typical Crane Installation

•
Serviceability often controls design as
opposed to strength

•
Steel and weldment fatigue is a major
serviceability issue

•
Therefore, serviceability dictates cost


Crane Serviceability Controls


References for Bridge Cranes

•
CMAA Standard 74 (Single Girder TR and UH
Cranes)

•
CMAA Standard 70 (Double Girder TR Cranes )

•
Call (704) 552
-
8644 to order

•
About $40 each


CMAA Standards 70 and 74



Interior Partitions & Ceiling
Considerations

•
Suspended ceilings will telegraph roof
deflections


Sprinkler Heads Indicate
Deflection

•
Common winter callback

•
May or may not indicate a real problem


Interior Partitions & Ceiling
Considerations

•
Suspended ceilings will telegraph roof
deflections

•
Noticeable

–
in large open offices

–
junctions of ceilings & interior walls


Typical Ceiling Problem

Interior Partitions & Ceiling
Considerations

•
Suspended ceilings will telegraph roof
deflections

•
Noticeable

–
in large open offices

–
junctions of ceilings & interior walls

•
Don’t tie interior partitions to main framing


Good and Bad Details

Bad Good

Interior Partitions & Ceiling
Considerations

•
Suspended ceilings will telegraph roof
deflections

•
Noticeable

–
in large open offices

–
junctions of ceilings & interior walls

•
Don’t tie interior partitions to main framing

•
Remember
-

Actual deflections are as much as
25% higher than calculations indicate

Roof Considerations

•
“L/Span” deflections


Comparison of L/Span
Deflections

•
L/180 on typical Z
-
purlin

–
20 foot bay = 1.33 inches, 30 foot bay = 2
inches

•
L/240 on typical roof bar joist

–
30 foot bay = 1.5 inches less initial camber of
3/8

–
Net deflection is 1.125, much less than Z
-
purlin

•
Z
-
purlin deflection is magnified by “purlin
roll”

Purlin Deflection



Roof Considerations

•
“L/Span” deflections

•
Purlin deflection at eaves and rakes


Eave Deflection/Ice Dam

Roof Considerations

•
“L/Span” deflections

•
Purlin deflection at eaves and rakes

•
Ponding, with low slope roofs


Ponding

•
Common failure type of joist roofs due to
clogged drains, scuppers

•
Can be caused by snow drifting

•
Design checks for stability failure are usually
not required for slopes of 1/4/12 or greater

•
Stability checks may be required for slopes
of 1/4/12 or greater if ice dams/snow drifts
occur…Be Careful with this condition!


Ponding Problem on 1/2 to 12 Slope



Roof Considerations

•
“L/Span” deflections

•
Purlin deflection at eaves and rakes

•
Ponding, with low slope roofs

•
Panel distress & leakage caused by
excessive purlin or frame deflections…this
may be first “clue” of serviceability issue


Non
-
Deflection/Drift
Serviceability

•
Expansion/Contraction

•
Not usually an issue with all steel building

•
Watch for adjacent structure

•
Watch for collateral materials..tilt
-
up
concrete especially


Non
-
Deflection/Drift
Serviceability

•
Camber

•
Corrosion

•
Vibration

•
Connection Slip


Summary

•
MBMA states that is up to owner (or his
agent) to identify all materials so that the
metal building can be designed to be
compatible

•
Know your owner/customer

•
Don’t forget to “program” the job in the rush
to start a design build job

•
Require that manufacturer meet AISC “Steel
Design Guide 3”



AISC “Steel Design Guide 3”

•
Call AISC 800
-
644
-
2400

•
Price $16


Questions????


Thank You!...Needham &
Associates

Consulting Engineers

http://www.needhamassoc.com


233 W. Baker St.

Fort Wayne, IN 46802


(219)420
-
3400


8417 Santa Fe Dr.
Overland Park, KS 66212


(913)385
-
5300