CONSTRUCTION FORUM

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Scaffolding: Safety, Design, and Construction Issues

Soliman Khudeira, Ph.D., S.E., P. E.Project Director with Chicago Dept. of Transportation, Division ofEngineering.

Introduction

On March 9, 2002, three women were killed when a suspendedscaffold fell from the 42nd floor on their car during high winds.Eight others were injured, of whom one who later died. The scaf-folding was used by a façade cleaning and window-caulking crewworking on the exterior of the 100-story John Hancock building,Chicago’s third-tallest building.

The scaffold was stored at the 43rd floor. The accident oc-curred when a wind gust exceeded 58 mph �according to the Na-tional Weather Service� and no work was under way. But afterbreaking loose from the tower, a portion of a suspended alumi-num platform fell 42 stories to the street. A section of the stagingremained suspended from the adjacent face of the building. Win-dows were smashed in the incident �Fig. 1�.

This narrative briefly compares the 2002 Chicago MunicipalCode related to scaffolding before and after the accident. Themain purpose of this narrative is to provide a forum for furtherdiscussions within the structural engineering community on scaf-folding safety, design, and construction issues.

ASCE/SEI 7-05 Wind Pressure on Scaffolding

According to section 6.4 of ASCE/SEI 7-05 �ASCE 2006�, thewind load on “Component and Cladding” using Method 1, Sim-plified Procedure is

Pnet = � · Kzt · I · Pnet30

where Pnet�wind pressure on a component or cladding �psf�;��adjustment factor for building height and exposure;Kzt�topographic factor evaluated at mean roof height �h�;I�importance factor to account for the degree of hazard to humanlife and damage to property; and Pnet30�net design wind pressurefor exposure B at h=30 ft and I=1.0. Minimum value for Pnet30

=10 psf acting in either direction normal to the surface.Scaffolds are occasionally covered with plastic sheets to pre-

vent construction equipment from falling or to act as weatherprotection for workers. Wind loads acting on scaffolds are in-creased significantly because of these covers and should be ac-counted for when determining the wind pressure on the scaffoldand ties. In the case of fixed scaffolds �supported by the ground�,it was found �Ohdo and Kareem 2000� that the system reliabilityhas increased significantly by increasing the number of ties thanby changing attachment configuration. Scaffold failure is oftenattributable high stresses acting on the ties, rather than on theframe, since stresses acting on the frame are relatively smaller

than those acting on the ties �Ohdo and Kareem 2000�.

PRACTICE PERIODICAL ON STRUCTU

Pract. Period. Struct. Des. Con

Chicago’s Scaffolding Code Requirement beforeand after the Accident

Up to the date of the accident, Chicago did not require permits forscaffolds, but city code requires that scaffolding “be so con-structed as to ensure the safety of persons working on or passingunder or passing by the scaffold.” After the accident, Chicagobuilding officials reviewed the regulations to determine if addi-tional safety guidelines are needed to protect workers and thepublic. As a result, a scaffolding ordinance was introduced andpassed the city council on July 31, 2002. The ordinance, then, wasincorporated into the Municipal Code of Chicago by adding anew Chapter 13–34 regulating scaffolding �City of Chicago2007�. Preexisting scaffolding-related code provisions are con-solidated into this new chapter. A summary of the ordinance is asfollows:• “Scaffold” or “scaffolding” shall mean temporary elevated or

suspended work units and their supporting structure�s�, usedfor supporting one or more workers or materials or both.Aerial buckets, one-person harnesses, and ladders used singly�e.g., without platforms or ladder jacks�, shall not be consid-ered to be scaffolding for purposes of this chapter.

• Construction: All scaffolding shall be so constructed as to en-sure the safety of persons working on or passing under orpassing by the scaffolding.

• Safeguards: All scaffolding shall be constructed, maintained,and disassembled in a manner that follows accepted engineer-ing practice and manufacturer’s specifications. “American Na-tional Standard ANSI A10.8-2001 Safety Requirements forScaffolding,” as amended, and “American Society of Me-chanical Engineers, ASME A/20.1-2001 Safety Requirementsfor Powered Platforms for Building Maintenance,” asamended, shall be considered accepted engineering practice, as

Fig. 1. Section of scaffold hanging from side of John HancockBuilding

RAL DESIGN AND CONSTRUCTION © ASCE / AUGUST 2008 / 109

str. 2008.13:109-110.

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shall other national standards deemed applicable by the build-ing commissioner.

• The scaffolding operator would be required to obtain a state-ment signed by a structural engineer certifying that the scaf-folding is structurally sound and that the method of assemblyadheres to accepted engineering practice and manufacturer’sspecifications or American National Standards Institute�ANSI� safety requirements for scaffolding.

• Anyone who erects, maintains, and uses scaffolding must com-plete a training course on scaffolding safety. The trainingcourses are offered at local colleges, but they must be preap-proved by the Chicago Department of Buildings.

• Architects and engineers on a jobsite on a scaffold also need tohave scaffolding safety training since each is considered a“user.”

• “Operator” is defined as the person erecting, maintaining, orusing scaffolding.

• The safety training courses consist of three different programs;operators will attend one four-hour training course and erec-tors will attend a full-day training course. The three programsareI. Scaffold Training for Supported and Suspended Users

�4-hour program�.II. Scaffold Erector Compliance and Safety Seminar-

Supported Scaffolds �1-day scaffold erector class�.III. Scaffold Erector Compliance and Safety Seminar—

Suspended Scaffolds �1-day scaffold erector class�.• The proposed ordinance requires property owners to obtain a

permit and provide a schedule for the intended use of thescaffolding before the work can begin.

• Those who will be using the equipment will be required toobtain a $1 million certificate of liability insurance before theerection of the scaffolding can begin.

• Scaffolding permit is required when scaffolding is being usedin a building in the City of Chicago that is either �1� locatedwithin the central business district, and is over 40 above grade;

or �2� any building over 80 above grade.

110 / PRACTICE PERIODICAL ON STRUCTURAL DESIGN AND CONSTRU

Pract. Period. Struct. Des. Con

• The scaffolding or “swing stage” must be lowered to either theground level and secured, or raised to the roof line and securedduring windy conditions when wind gusts exceed a velocityidentified in the manufacture’s specifications as posing ahazard.

• During periods of nonuse—defined as more than 2 hours—scaffolding must be safely and securely attached to the build-ing in accordance with federal regulations, ANSI standards,and the manufacturer’s specifications.

• If the scaffolding will remain on a building for 6 months orlonger, then an affidavit would need to be executed by theoperator verifying that the scaffolding is being operated andmaintained in full compliance.

Since the incorporation of the Scaffolding Ordinance in the Chi-cago Municipal Code, Chicago has avoided other scaffolding ac-cidents similar to the John Hancock building incident.

Summary

This narrative provides an overview of the Chicago scaffoldingordinance before and after a major accident. The narrative is onlyintended as a means to open a forum for additional discussions onthe subject. The readers are invited to discuss other issues andordinances related to design requirements and construction safetyimplemented in other major cities.

References

ASCE. �2006�. Minimum design loads for buildings and other structures,ASCE/SEI 7-05, ASCE, Reston, Va.

City of Chicago. �2007�. City of Chicago municipal code, Title 13, Chap-ter 13–34.

Ohdo, K., and Kareem, A. �2000�. “Reliability analysis of constructionscaffolding systems under wind storms.” Proc. 8th ASCE Conf. onProbabilistic Mechanics and Structural Reliability, PMC2000-329,

Reston, Va.

CTION © ASCE / AUGUST 2008

str. 2008.13:109-110.