Journal of Constructional Steel Research 65 (2009) 422–435 Contents lists available at ScienceDirect Journal of Constructional Steel Research journal homepage: www.elsevier.com/locate/jcsr Experimental and analytical studies on steel scaffolds under eccentric loads Jui-Lin Peng a , Kuan-Hung Chen b , Siu-Lai Chan c,∗ , Wei Tong Chen a a Department of Constr. Engrg., Yunlin University of Sci. and Technol., Touliu, Yunlin, 640 Taiwan, ROC b Central Taiwan Science Park Administration, National Science Council, Executive Yuan, Taiwan, ROC c Department of Civil and Struct. Engrg., Hong Kong Polytechnic University, Hong Kong, China article info Article history: Received 25 August 2007 Accepted 25 March 2008 Keywords: Critical load Eccentric load Scaffold Scaffolding abstract Steel scaffolds collapse quite often in many places with a considerable number of reported casualties, but their behaviour has not been studied to the extent of many other permanent structures. This paper investigates the effect of eccentric loads on steel scaffolding systems used in construction sites. The type of scaffold considered here is the door-shaped steel scaffold with an inner reinforced gable sub-frame. The single-side cross-brace scaffolding systems with various eccentric loads are mainly focused on two issues, namely, the unrestrained boundary and the removal of cross-braces at the access location. This study shows that regardless of the lowest layer of cross-brace in a scaffold being removed or not, the critical load of a scaffolding system under an eccentric load is the lowest, whereas that of scaffolding system under a concentric load is the maximum. If the bottom jack base of a scaffolding system in construction sites is strengthened to a fixed end, the critical load of this scaffolding system will be greatly increased. If a scaffolding system is erected more than 8 stories high, the critical load of the scaffolding system with the fixed end base can be increased to 2.4 times that with the hinged base. However, whether the cross-braces at the lowest story of a scaffolding system are removed or not, the simulated scaffolding test indicates that the critical load of a used scaffolding system under the eccentric load is the lowest and its load reduction also appears significant. © 2008 Published by Elsevier Ltd 1. Introduction During the construction of buildings, steel scaffolds are used for two purposes – one is the “scaffolding system” for finishing of the facade, while the other is a “shoring system” in support of construction loads. When used as a scaffolding system, the steel scaffold is frequently used as equipment auxiliary to related works in construction sites. For instance, in processing works such as assembly and disassembly of vertical formworks and plastering work on facades, the scaffold can provide a good working site for the workers. When applied as a shoring system, the steel scaffold works as a falsework system for supporting the construction loads of the freshly placed concrete, steel, formwork and crews on the slab during construction. The setups of the two purposes are different. Fig. 1 indicates that under normal condition, the steel assembly scaffold installed in construction sites as shown is used as a working scaffolding system. In Fig. 2, the assembly of the steel scaffold is for using as a shoring system in support of construction loads on the slab. The most significant difference between the two systems of scaffolds is that when the system is ∗ Corresponding author. Tel.: 852 27666047; fax: 852 23346389. E-mail address: ceslchan@polyu.edu.hk (S.-L. Chan). used as a “scaffolding system”, it is erected in a single row and, secondly, cross-braces only exist on the one side. When the system is used as a “shoring system,” it is erected in multiple rows and, secondly, cross-braces exist on both sides. Further, according to the survey of a scaffolding system used in construction sites in Taiwan, a scaffolding system set up in construction sites frequently has no restraint at top stories. This greatly differs from the “shoring system” where its top horizontal formwork is restrained [1]. Since scaffold systems are erected in a single row in construc- tion sites, works are frequently processed at the edge closest to the building when workers perform operations such as installing the vertical formwork and plastering the façade of buildings. This causes the scaffolding system to bear an eccentric load. The dis- crepancy between such an eccentric load and the concentric load really is worthy of a study into the influence of eccentric loads to the critical load of the scaffolding system erected as a single-row. Fig. 3 shows a collapse case of scaffolding system in a construction site in southern Taiwan. At present, the experimental studies of critical loads of steel scaffolds have a common drawback [2–5]. Tests have to allow for the limitation of laboratory facilities with a hydraulic thrust headthat only operates in a single direction. This leads to critical loadstudies of these scaffolds under the restrained boundary condition without any eccentricity load and with lateral restraint at the top. This type of concentric load with a lateral restraint 0143-974X/$ – see front matter © 2008 Published by Elsevier Ltd doi:10.1016/j.jcsr.2008.03.024