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
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