01.14: Tests of alternately loaded single‐cut joints with blind bolts

Abstract

Joints in the frames designed with the cold-formed profiles with a thickness 4÷5 mm, formed by a lap connection of their members by means of mechanical fasteners, are characterised by a considerable degree of flexibility. In static calculations of exemplary bearing structures resistance of the joints was included on the basis of experimentally established relations: force-deformation and moment-rotation, that vary nonlinearly under the influence of loads. Some of this loads, e.g. wind, may change their direction. Then, the effects of the next variable load are superimposed on action of the permanent load and effects of previously existing cycles of the variable actions. In a given joint of a bar structure the directions of resultant forces acting on the individual fasteners are changing, and its behaviour is described by defined hysteresis loops. Calculations of such a structure requires i.a. incremental load-deformation analysis. Then, internal forces in particular members and deformations in the joints may be significantly different from the case, when horizontal wind load acts only in one direction. To describe the behaviour of a bar structure with the flexible joints loaded alternately, it is necessary to develop an experimentally verified method for prediction of hysteresis loops for the joints loaded by shearing force and bending moment. Appropriate design procedures of such joints, including proper criteria of their strength and limit deformation are needed. The paper presents the preliminary results of the tests of the specimens with the alternately loaded joints, in which the cold-formed profiles are connected by means of proper number of the blind fasteners BOM type. The alternating load of the joint in the test specimen -simultaneously by the shearing force and bending moment -change the direction of the resultant forces, acting on the individual fasteners. Values of the load and its history have been selected to correspond the situation, which may occur in the actual structure of the frame loaded simultaneously by the permanent load, snow and wind. Results of tests are presented on the diagrams of relation: force-deformation in the axis of the individual fastener and moment-rotation in the joint. The preliminary conclusions are formulated and program of further investigations is presented. The aim of the research is to develop the structural system of lightweight steel buildings with latticed bearing structures.

Study on Bolted and Blind-Bolted Single Shear Connections of Cold-Formed Steel Members

“…The behaviour of such structures loaded alternately, e.g. by wind, may also raise some concerns, and require appropriate consideration in the static calculations of the bearing structure [21].…”

“…The structural response of a CFS frame with semi-rigid blind-bolt joints were discussed by Swierczyna and Wuwer in [2]. Paper [21] presents the results of tests of connections in alternating load. A summary of previous activities in this area is included in [4].…”