Experimental investigation of preload losses in high strength bolts under cyclic loading

Slip-resistant shear connections with preloaded bolts have traditionally been used in steel structures exposed to cyclic / fatigue loading or in cases when bolt slipping or connection deformations should be restricted. Hence, shear load is transferred through friction surfaces rather than through contact between the bolt surface and the hole. The main influencing parameters determining slip resistance of the connection are the friction between contact surfaces and the bolt preload level. This paper presents an experimental study of preloaded bolted connections under cyclic load, the main objective being to investigate the influence of cyclic load on the losses of preload force in high strength bolts and lock bolts.

A State-of-the-Art Review on Hybrid GFRP-Concrete Bridge Deck Systems

The state-of-the-art review of hybrid GFRP-concrete systems for bridge decks is presented in this study. Previous research on the experimental work, analytical modeling, and field application on hybrid GFRP-concrete deck systems are presented, along with a variety of deck systems are discussed. Then, seven typical types of connection technology between FRP and concrete are introduced and compared. Besides, the current progress on the performance of shear connections via beam tests, pushout tests, and pullout tests are probed, respectively. Finally, general conclusions are made, identifying the need for future research.

BEARING STRENGTH OF SHEAR CONNECTIONS FOR TUBULAR STRUCTURES: AN ANALYTICAL APPROACH

This work deals with the prediction of the bearing resistance of elementary shear connections constituted by gusset plates and square hollow sections fastened with long bolts. The research is motivated by the lack of specific rules in international codes for this particular configuration. In fact, while in lap shear connections, single or double-sided, the holes are always confined out of plane, in case of connections with long bolts and gusset plates (typical of tubular structures), the holes are constrained out of plane outwards, but they are free to buckle inwards, providing a reduction of the bearing strength. Within this framework, the paper is aimed at the development of an analytical formulation for the prediction of the bearing resistance of connections with long bolts and square hollow sections (SHS). The proposal is based on the calculation of the post-buckling load of the tube plate subjected to bearing at the bolt hole, combining the Winter's formula (originally developed to predict the post-buckling strength of steel plates accounting for geometrical and mechanical imperfections) with a simplified FE model developed in SAP 2000. The procedure developed is presented in detail proposing a design equation for connections with long bolts, based on a formula suggested recently by Može (2014, 2016) suitable for the inclusion in code provisions such as EC3. The accuracy of the design equation is checked on the experimental data reported in a previous work of the same authors properly extended with parametric FE simulations to cope for variation of geometrical parameters.