IRSST - Institut de recherche Robert-Sauvé en santé et en sécurité du travail

Evaluation of a Horizontal Lifeline System, Anchorage Connectors and Braced Trusses as Host Structure for Residential Roofing Work

Abstract

Construction workers who install roof trusses are at risk of falling because they have to work at height in difficult conditions. Poised precariously on the framework, they may lose their balance or fall when putting trusses into place. To protect his workers from falling while installing trusses, plywood or shingles, a residential builder recently developed a horizontal lifeline system (HLLS) consisting of two aluminum posts and a steel cable using the roof they are erecting as the host structure. The HLLS, although operational, is cumbersome and not very user-friendly, which is keeping it from being used on construction sites. Yet preliminary testing on a roof on which work had been completed showed that the system has potential as a component of a fall-arrest system. So at the request of the sector-based OHS association ASP-Construction, the Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST) conducted this study with the aim of evaluating the HLLS to make it more effective, user-friendly and reliable by improving the installation method and making it lighter. A second aim of the study was to confirm the strength of braced roof trusses as a host structure for a worker’s lanyard, the HLLS and anchoring connectors certified to standard CAN/CSA Z259.15 – Anchorage Connectors.

To do so, (1) a structured analysis of the HLLS was done in compliance with standard CAN/CSA S157 – Strength Design in Aluminum, (2) fall testing to confirm the HLLS’s strength was done on a structure in a laboratory at Polytechnique Montréal and (3) fall testing to confirm the strength of the trusses as a host structure for the HLLS and CAN/CSA Z259.15-certified roofing anchorage connectors was done on braced roof trusses rebuilt at the Polytechnique Montréal lab. The fall testing met the requirements of standard CAN/CSA Z259 respecting fall protection.

Initially, when the host structure was being rebuilt in the lab, the trusses were to be braced following the recommendations of the Association québécoise des fabricants de structures de bois (AQSFB) or those of the Centre d’expertise sur la construction commerciale en bois (CECOBOIS), but the residential building contractor informed us that in practice, contractors almost never follow the recommendations of those two organizations when bracing trusses, preferring a tried and tested method instead. So there was no point testing the strength of a host structure braced according to the recommendations of the AQSFB or CECOBOIS, because they are not followed on construction sites. It was therefore decided to brace the rebuilt structure following the usual practice on jobsites, document the setup and test its strength as a host structure for the HLLS and CAN/CSA Z259.15-certified anchorage connectors.

The HLLS passed all the fall tests and therefore met the performance and strength requirements for such a system. The results of the dynamic fall tests showed that

  • the 127 mm x 127 mm x 6.4 mm aluminum HSS posts serving as uprights for the HLLS passed all the dynamic fall tests as an anchorage for a lanyard;
  • the HLLS consisting of 127 mm x 127 mm x 6.4 mm HSS posts and a DBI SALA Sayfline passed all the dynamic fall tests as a fall arrester;
  • the trusses braced according to current practices on construction sites passed all the dynamic fall tests as the host structure for a worker’s lanyard with the 127 mm x 127 mm x 6.4 mm HSS as anchorage;
  • the trusses braced according to current practices on construction sites needed reinforcement in order to pass the tests. The structure with the reinforced bracing passed all the dynamic fall tests as the HLLS host structure with 127 mm x 127 mm x 6.4 mm HSS posts as system uprights;
  • the trusses braced according to current practices on construction sites passed all the dynamic fall tests as the host structure for DBI, Protecta and Ridge CSA Z259.15-certified anchorage connectors. The results obtained with these three types of connectors indicate that reinforced braced trusses form an appropriate structure to which to attach CAN/CSA Z259.15-certified anchorage connectors.

Furthermore, the contractor’s HLLS was improved by reducing the number of parts to make it easier to secure it to the host structure. This also reduced the system’s weight by at least 30%. The HLLS gives workers greater mobility and protects them the entire time they are working, while also enhancing productivity. It therefore provides good protection against falls from heights for residential roofers. The cable turnbuckle from the original version of the contractor’s HLLS was removed in the study version to cut costs and facilitate testing, as it has no structural function. This improved version of the cable system, checked and validated by tests that meet the requirements of standard CSA Z259 respecting fall protection, will make it easier to use on construction sites.

Additional Information

Collection: Scientific reports
Category: Research Report
Research Project: 2013-0047
Online since: January 20, 2017
Format: Text