PPT_AvoidProbSpfyMetalRoofNov2010

Alexander Newman, P.E. Exponent Failure Analysis Associates (508) 652-8533

Structural Renovation of Buildings 1

1

Your site coordinator received information on how to register your PDHs earned along with the log-in information and should forward to all site attendees

It is important that you log-in to the ASCE website and follow the steps for recording your PDHS

At the end of the online process you will receive a confirmation, be sure to print this page for your records

Also, please record the state(s) you carry a P.E. license. Your P.E. license information only needs to be recorded once.

Should you have questions, please contact: [email protected]

Participants, please note that a New ASCE PDH reporting process is in effect:

2

Avoiding Problems in Specifying Metal Roofing

ASCE Web SeminarPresented by Alexander Newman, P.E.

Copyright 2006-2010 Alexander Newman.

All rights reserved.

Reproduction of this material without a written permission

of the copyright holder is a violation of the U.S. law



3

Introduction

We Will Cover the Following Topics Various types of metal roofing and their uses Seam configurations The role of metal roofing in building structure Specification pitfalls Avoiding metal roofing failures Renovation of metal roofing A short case study Conclusion, Q & A

4

IntroductionAdditional Reference Sources:

Two-day ASCE Seminar: Design of Metal Building Systems: Avoid Pitfalls in Specifying and Procuring

A. Newman, Metal Building Systems: Design and Specifications, 2nd ed., McGraw-Hill, 2004

MBMA Metal Roofing Systems Design Manual, Metal Building Manufacturers Association, Cleveland, OH US Army Corps of Engineers, TI 809-29 (1998),

Structural Considerations for Metal Roofing A. Newman, Metal Roofing: A Primer for Engineers,

Structure, Sept. 2006

Manufacturers literature



5

IntroductionWhere Metal Roofing is Used First used in conventional buildings

Drayton Hall, Charleston, SC

Historic Charleston, SC

6

IntroductionWhere Metal Roofing is Used, Contd Then, MBS

Hydrant Fueling System at Travis Air Force Base. Vacacille, CA (USACE)



7

IntroductionWhere Metal Roofing is Used, Contd and conventional buildings again

PGC, MD

8

Uses and Types Various Metal Roofing Classifications Water-shedding vs. waterproof

Architectural vs. structural

Through-fastened vs. floating (concealed or standing-seam)

Water-Shedding vs. Waterproof Slope requirements



9

Uses and Types Architectural vs. Structural Both look good the type depends on the need for substrate

Architectural needs substrate

Structural functions similarly to metal deck, carries loads in flexure

Through-Fastened vs. Standing-Seam (Floating or Concealed-Clip)

10

Structural Loads on Metal Roofing

Structural Loads on Metal Roofing Snow



11

Structural Loads on Metal Roofing

Structural Loads on MBS, Contd Wind

Temperature

Change in unit stress = E e t

12

Structural Loads on Metal Roofing Load Path from Roof to Foundation



13

Uses and Types

Seam Configurations

Metal Architecture

14

Uses and Types

Seam Configurations Lapped

Batten



15

Uses and Types

Seam Configurations Vertical

Tile look-alike

16

Uses and Types Vertical-Seam Roofing Architectural and structural

Good for complex configurations

Most vulnerable at hips and valleys



17

Uses and Types

Through-Fastened Roofing Oldest, inexpensive design

Corrosion-res. fasteners w/ neoprene washers

18

Uses and Types Through-Fastened Roofing, Contd Typically, structural type

Offers some diaphragm action

Ral del ToroExposed fasteners (rust)rsNeoprene washers may not be water tight



19

Uses and Types

Through-Fastened Roofing, Contd Problem: Thermal expansion-contraction

Max. span = 60 ft?

Slotted pre-punched holes help

20

Uses and Types Through-Fastened Roofing, Contd Relying on purlin roll to reduce damage??

Most metal building manufacturers rely upon purlin roll to reduce slotting of the roof panels. (AISC Design Guide No. 3, 2nd ed, p. 11)

Ral del Toro



21

Uses and Types Through-Fastened Roofing, Contd Using rigid insulation?

22

Standing-Seam Roofing

Standing-Seam Roofing Snap-on v. rolled seams Clip height must match roofs Seam configurations: Vertical and trapezoidal

Ral del ToroNever do this!



23

Standing-SeamRoofing Clips For clip spacing and

fasteners, consult UL Roofing Materials & Systems Directory

Closer clip spacing in high-wind roof areas

Metal Architecture

24


Clips, Contd A 100-ft-long piece of steel will expand/contract by ~ 0.78 in.

under a temperature change of 100o F. Alternatively, if prevented from expansion by fixed supports, the same piece will build up an added stress of about 19 ksi!

Expansion capacity of the clips This means that the maximum length of roofing that can freely

move under a temperature change of 100o F is only about 128 ft in each direction.

Stepped expansion joints may be needed beyond these limits



25

Standing-Seam Roofing Standing-Seam Roofing Construction Some through-fastening is still needed (where?)

26


Standing-Seam Roofing Details Snap-on v. Pittsburgh double lock trapezoidal seams

Metal Architecture



27

Purlin Bracing by Roofing?

Why Purlin Bracing is Needed What can provide it?

- Discrete bracing: angle, strap, channel

- Through-fastened roof + liner panels

Bracing for uplift conditions from wind and gravity

28

Purlin Bracing by Roofing?

Three Functions of Purlin Bracing(AISI Spec. Sec. D3)

1. Provide lateral bracing for members compressive flange

2. Restrain member from rotation (torsion from load, suspended items)

(AISI Spec. Comm. to Sec. D3.2.1)

3. Restrain the whole assembly of purlins and roofing from lateral translation



29


Some Limitations of Standing-Seam Roofing Limited diaphragm action and purlin bracing

Complex roof plans, hips, openings restrict movement

Trapezoidal: Difficult transitions, cannot be curved

but despite all this, still the best

30

Minimum Slope

Minimum Recommended Slopes for Various Types of Metal Roofing

Slope %

Slope, in./ft.

Panels with water-shedding joints, except as listed belowArchitectural (non-structural) and structural panels wider than 305 mm (12 in.)

33 4

Panels with underlayment or with joints > 2 in. highArchitectural panels, and structural panels no wider than 305 mm(12 in.), both with underlayment and with seams at least 38 mm (1in.), but less than 51 mm (2 in.) high Architectural panels with seams at least 51 mm (2 in.) high, with underlayment; and structural panels no wider than 305 mm (12 in.) with seams at least 51 mm (2 in.) high.

Where the ground snow load is more than 98 kg/m2 (20 psf)Where the ground snow load is 98 kg/m2 (20 psf) or less

25

2517

3

32

Waterproof panels

Where the ground snow load is more than 98 kg/m2 (20 psf) Where the ground snow load is 98 kg/m2 (20 psf) or less

84

1

(Adapted from US Army Corps of Engineers TI 809-53, 1999.)



31

IBC Provisions

Min. Roofing Slopes per IBC-06, -09 (Chap. 15) Lapped without sealant 3:12

Lapped with sealant :12

Standing-seam :12

Fasteners per IBC Chap. 15 Galvanized or SS

Pros and Cons of High Slope Space to be heated/cooled

.

32

Panel Materials and Finishes

Panel Finishes Need: resistance to corrosion, fading, peeling, cracking

Galvanizing is now obsolete; Galvalume prevalent

Aluminum coating: a physical barrier

Galvalume (55% Al, + 45% Z) and Galfan (5-95)

Separate Z from unprotected steel

Sheet Al, Copper, Stainless Steel



33

Panel Materials and Finishes

Panel Coatings Least expensive: Acrylic & polyester paints (3-5 yr warr.)

Siliconized polyesters (10-yr warr.)

Best: Fluorocarbon-based coatings, such as polyvinylidenefluoride (PVDF), e.g., Kynar 500 and Hylar 5000 (20-yr warr.)

Typ. thickness: 1 mil nominal (0.9 actual)

Use 2 or even 4 mils for severe cases?

Most damage at cut edges, penetrations

Excellent: New PVC Plastisols, applied > 4 mils

34

Wind Uplift Ratings

Wind Uplift Ratings: UL 580 10 x 10 sample edges sealed at perimeter

Alternating wind pressure and suction

Three classes:

Class 30 (100 mph for 80 min.)



For Class 90, specimen sustains 105 psf uplift for 5 mins

Static test does not consider wind gusts



35

Wind Uplift Ratings

Wind Uplift Ratings: FM 4471 Also covers durability and resistance to corrosion, fire, leakage,

hail

Uplift only; 12x 24 specimen; edges sealed at perimeter

Ratings 1-60, 1-90, 1-120, 1-150, 1-180

E.g., a panel rated 1-90 must sustain 90-psf uplift for 1 min.

Again, static test does not consider wind gusts

36

Wind Uplift Ratings

Wind Uplift Ratings: ASTM E 1592 C. 1994 covers metal panels and anchors

Static loading to failure

10 x 25 specimen, no clamping at edges, panels free to move

Preferred test today



37

Wind Uplift Ratings

Limitations of Tests All these are static what happens in a distorted panel

IBC-06 (Sec. 1504.3.2) requires testing of metal roofs by UL 580 or ASTM E 1592 (except structural roofing can be designed and tested per AISI Cold-Formed Spec.)

38

Tips for Specifiers Specifying Metal Roofing SSMR with Pittsburgh double lock work best

Minimize equipment, pipes, penetrations

Underlayment: drain and detail penetrations

Remember min. slope requirements

Require submittals of details



39

Tips for Specifiers

Metal Roofing in Snow Regions Snow deflects roofing, allows standing water to back up

Use waterproof roofing to reduce ice dams

Increase min. slope requirements to 2:12?

Use snow guards with Pittsburgh double lock seams

Design roofs with snow guards for flat-roof snow?

Snow guards can keep snow still, cannot stop a slide

Consider parallel-to roof load on fasteners from snow drag force

40

Tips for Specifiers Curved Roofing

USACE

Scottsdale Museum of Contemporary Art



41

Avoiding Roofing Failures Failures Caused by Wind Total collapse v. roofing failure

Read Performance of Metal Buildings in High Winds by Institute for Business & Home Safety, No. 9 Jan. 1999, http://www.ibhs.org/research_library/downloads/137.pdf

Pensacola, FL, 9/20/04-- A building that stored boats is damaged by Hurricane Ivan (FEMA)

42

Avoiding Roofing Failures Failures Caused by Wind, Contd Components and cladding wind in previous codes vs. todays

New Orleans, Hurricane KatrinaGUAM, December 15, 2002 -- A church receives major damages on the island of Guam caused by Supertyphoon Pongsona (FEMA)



43

Avoiding Roofing Failures Failures Caused by Wind, Contd Damage at eaves & roof corners

44

Avoiding Roofing Failures Failures Caused by Snow Design- or construction- related



45

Avoiding Roofing Failures Design-Related Snow Failures Improperly specified roof loading

Overly low-slope (1/4:12) roofing allows for ice buildup at the eaves => leakage and overload

46

Avoiding Roofing Failures Leakage Most vulnerable: Valleys, hips, edges



47

Avoiding Roofing Failures

Construction-Related Field Problems

48

Avoiding Roofing Failures Field Problems, Contd



49

Avoiding Roofing Failures Field Problems, Contd

50

Avoiding Roofing Failures

Proper Maintenance Helps Avoid Leaks



51

Renovating Roofing Renovation of Metal Roofing Check min. slope reqs for water-shedding & waterproof roofing

Typ. problems of through-fastened roofs:

- Penetration by screws => leakage

- Backed-out fasteners

- Rust and failed finish, displaced trim.

Cost of proper roof renovation may exceed original construction cost of roof!

52

Renovating Roofing

Renovation of Metal Roofing, Contd Roof evaluation

- Condition of fasteners critical.

- Spacing by USCE: 8end, 12 side laps.

Recoating by brushing or spraying.



53

Renovating Roofing

Renovation of Metal Roofing, Contd Recoating by brushing or spraying.

Reroofing with standing-seam roofing

If old roof removed, add purlin bracing and diaphragm.

200-250 ft max roof run

54

Renovating Roofing

Renovation of Metal Roofing, Contd Reroofing w/ through-fastened roof

- Fitting the new roof over old

- Remove old roofing or not?

- Are purlins rusted?

- Attach to purlins, not old roofing.

- Elevate new roofing with blocking (or channels or Roof Hugger).



55

Renovating Roofing Renovation of Metal Roofing, Contd Using retrofit framework for slope change: over existing purlins,

perpendicular to purlins, column-to-column

EOR: structural evaluation of roof, assumes post spacing.

56

Renovating Roofing

Renovation of Metal Roofing, Contd Check building for wind on new gables

Bracing purlin, roof, and vertical

Require anchorage details for actual conditionsmost problems are at the interface

Code reqts for new space (egress, vent, fire)

Dealing w/ existing HVAC units.



57

Renovating Roofing

Renovation Checklist Governing code and edition

Design loads and load combinations

Allowable deflection and drift limits

Information about existing building and any requirements for itsstrengthening

Plans, sections, assumed details

Require submittal of shop drawings, including anchorage details,and structural calculations.

58

Roofing at Maintenance Garage:Original Concept

Case Study



59

Case Study

Changed Concept

60

Case StudyFinal Product



61

Alexander Newman

[email protected]

Q & A

Documents

PPT_AvoidProbSpfyMetalRoofNov2010