Structural behaviour and design of high strength steel tubular sections and tubular joints

Abstract

High strength steel (HSS) with nominal yield stresses higher than 450 MPa is increasingly popular in the infrastructure sector as an economical and sustainable construction material. The application of HSS in tubular structures which are widely used in onshore and offshore structures can reduce structural self-weight, construction costs and carbon footprints. Tubular members and tubular joints are basic components of tubular structures. Related research and design rules for HSS tubular sections and tubular joints are therefore imperatively needed in order to facilitate the structural application of HSS tubular structures. Design rules for HSS tubular sections in compression were proposed using the deformation-based continuous strength method (CSM). Non-slender and slender circular hollow sections (CHS), elliptical hollow sections (EHS), square hollow sections (SHS) and rectangular hollow sections (RHS) were investigated. Results of 277 tests in the literature were collated and a parametric study on 465 HSS tubular stub columns was conducted. The proposed CSM and codified design methods were assessed against the experimental and numerical results of 742 stub columns. The proposed CSM can produce more accurate and consistent strength predictions. Design rules for HSS tubular sections under bending were proposed using the CSM. Results of 146 tests in the literature were compiled and a parametric study on 660 HSS tubular beams was conducted. Base curves and resistance functions were proposed for non-slender and slender CHS, EHS, SHS and RHS. Test and numerical results of 806 tubular beams were used to assess the proposed CSM and codified design methods. Resistance predictions of the proposed CSM are more accurate and consistent. The structural behaviour and static strength of HSS RHS X-joints under axial compression in the braces were examined. Eight built-up RHS X-joint specimens which were composed of fabricated steel tubes with a measured yield stress of 907 MPa were tested. Finite element analysis on 599 built-up RHS X-joints in S460, S690 and S960 steel was conducted. The test results demonstrate sufficient deformation capacity and ductility of test specimens failing by chord face plastification. Effects of heat affected zones (HAZ) on the joint initial stiffness are minor but could significantly lower the joint strength. The CIDECT strength prediction is generally unconservative for chord face plastification and becomes conservative for chord side wall failure and combined failure modes of the both. Appropriate design rules were proposed for HSS RHS X-joints. The structural behaviour and static strength of HSS CHS X-joints under axial compression in the braces were investigated. Six CHS X-joint specimens with measured yield stresses up to 960 MPa were tested and numerical simulations on 724 CHS X-joints using S460, S700, S900 and S1100 steel were carried out. The failure mode of the CHS X-joints examined is chord plastification. The test results show that the deformation capacity and ductility of test specimens are sufficient. Effects of heat affected zones (HAZ) on the initial stiffness and static strength of the CHS X-joints are relatively insignificant. The CIDECT strength prediction is increasingly unconservative with increasing steel grade. Suitable design rules were proposed for HSS CHS X-joints.