Tension Test for Axially Vibrated Prestressing Fine-Rolled Screw-Threaded Steel Bars Based on Thread-Contact Connection

Xingu Zhong,Chao Zhao,Tianyu Zhang,Xiaojuan Shu,Mingyan Shen,Yohchia Frank Chen

doi:10.1155/2019/1806532

Abstract

The interface between anchor plate and anchorage nut can be considered as a coupling spring whose stiffness is essentially the contact stiffness related to normal force at the contact surface, thus removing the usual assumption of fixed connection. The nut threads and steel bar are also connected with a coupling spring with the stiffness determined based on the threads treated as cantilever components. An analytical model was developed to assess the axial vibration of an anchorage system consisting of prestressing fine-rolled screw-threaded steel bars (P/S FSSBs). Both laboratory model and field tests show that the contact stiffness between anchor plate and anchorage nut has good a linear relationship with the effective tension of prestressed tendons. The vibration model was used to obtain the natural frequency and tensile force of a P/S FSSB. It is shown to be feasible and practical. According to the analytical model and test method presented in this paper, the proposed tension tester for P/S FSSBs possesses the features of repeated use, rapid testing, and minimized impact on the construction and is thus suggested for wider practical applications.

Highlights

IntroductionPrestressing fine-rolled screw-threaded steel bars (P/S FSSBs) have been extensively used as vertical prestressing tendons in concrete bridges. e FSSB anchorage system consists of a FSSB, anchor plate with nut at the top and bottom, and exposed segment at the top, as shown in Figure 1 where the anchor plate and anchorage nut are in contact with each other and the nut anchorage section is connected with the FSSB through the threads. e effective tension of the FSSB affects bridge’s safety and durability significantly. e exposed section of vertical P/S FSSB including the nut section has been analyzed as a fully fixed cantilever beam by Zhong et al [1], in which a developed test method was used to measure the effective tension of the bar system by observing the natural frequency change in the exposed section
The contact between the anchor plate and anchorage nut is represented by a coupling spring whose sti ness is essentially the contact sti ness related to the normal force at the contacting surface, which lifts the usual assumption of xed connection. e FSSB and nut threads are connected by a coupling spring whose sti ness is calculated by treating the threads as cantilever components
An analytical model is proposed for assessing the axial vibration of the P/S FSSB anchorage system

Summary

Introduction

Prestressing fine-rolled screw-threaded steel bars (P/S FSSBs) have been extensively used as vertical prestressing tendons in concrete bridges. e FSSB anchorage system consists of a FSSB, anchor plate with nut at the top and bottom, and exposed segment at the top, as shown in Figure 1 where the anchor plate and anchorage nut are in contact with each other and the nut anchorage section is connected with the FSSB through the threads. e effective tension of the FSSB affects bridge’s safety and durability significantly. e exposed section of vertical P/S FSSB including the nut section has been analyzed as a fully fixed cantilever beam by Zhong et al [1], in which a developed test method was used to measure the effective tension of the bar system by observing the natural frequency change in the exposed section. E model presented in Figure 2 is Exposed segment of the vertical prestressed fine-rolling screw-threaded steel bar Nut. similar to the bolt fastening component used in mechanical engineering and pipeline engineering. Based on the deformation between screw rod and nut threads, a discrete model was developed to evaluate the axial vibration characteristics of a bolt fastener in a variety of mechanical connections [8,9,10,11]. Which the exposed section l2 of vertical P/S FSSB (Figure 2) consists of two mass blocks with the mass 0.5mr for each, which are connected by a coupling spring with the sti ness kr (Figure 3).

Model Parameters

Signal Testing of the Axial Vibration of FSSB

Conclusions