Seismic behavior of steel space truss connections to reinforced concrete supporting columns

Abstract

Roof joint is a critical connection in space truss structures, which connects the upper steel space truss roofs and reinforced concrete structures. Because of its simple structural detailing and easy construction, a typical kind of roof joint is comprised of four embedded anchor rods, a mortar layer, a base plate, and stiffeners are popular in small- to medium-span space truss structures. Among them, base plates with slotted bolt holes are commonly used to release the deformation caused by temperature change or earthquake input. The roof joints were considered either as pinned or rigid connections in the design. In this paper, quasi-static tests investigating the influence of the applied axial force and the shape of bolt holes on the shear resistance and seismic behavior of roof joints were performed. The roof joints exhibited semi-rigid connection behavior and two types of initial resistance mechanisms, sliding and overturning, were observed. With the increase of applied axial force, the behavior of roof joint changes from sliding to overturning. Finally, effective methods to determine the initial resistance mechanism and calculate the ultimate shear strength of roof joints are proposed. These findings and analyses may provide guidelines for roof joint design practice for space truss structures.

Effect of concrete edge distance on the hysteretic response of roof joint

“…More specifically, the displacement amplitude of loading is gradually increased, i.e., 2, 4, 6, 8, 10, 14, 18, 22, 26, and 30 mm. [55] For each displacement amplitude level, two cycles of loading were imposed. The experiment was terminated when the shear resistance of the specimen drops to 85% of the ultimate strength.…”

“…When the force of the roof joint is in the state of combined shear and bending, the calculation can be performed as per the mechanical model proposed by Cui et al, [55] as shown in Figure 10. In the model, the effects of friction, hole shape, anchor rod contribution, bending moment, axial force, and mortar strength are taken into consideration.…”

“…In general, the roof joint has two resistance mechanisms with different axial force. [55] When the roof joint is subjected to low axial loads, the base plate will slip until it contacts the anchor rods, then it will rotate around the anchor rods upstream. In contrast, under high axial loads, the base plate of the roof joint exhibits low ductility and barely any precursory slip as it rotates around the upstream anchor rods.…”

“…where F u is the ultimate shear resistance of the roof joint, F vy is the resistance by the anchor rod, V c is the shear resistance controlled by the concrete edge failure, and F RB is the rigid body resistance from the support. [55] 4.1 | Shear strength evaluation of anchor rods in roof joint…”

“…where n v is the number of anchor rod transferring shear force which can be calculate form mechanical model of roof joint proposed by Cui et al, [55] F V ar is the shear resistance transmitted by the anchor rod which is calculated by Equation (2a), and F M ar is the bending resistance which depends on the hole shape and can be determined by Equations (2b) and (2c) for circular and slotted hole base plate, respectively. M ab,p is the plastic ultimate moment of a single anchor, and t is the thickness of the mortar layer.…”