Axial compressive behaviour and design method of extra-large-diameter welded hollow spherical joints

Research on axial compressive behavior with circular steel tubes reinforced by sleeved tube

Behaviour of square hollow section brace-H-shaped steel chord T-joints under axial compression

A state-of-the-art review is presented of information on design, installation and performance of grouted piles. Grouted piles are finding increasing use as foundation elements for offshore structures where hard soil conditions, calcareous sands and/or deep embedment for high axial capacity preclude installation by conventional pile driving methods. Purposes of this study were to consolidate performance data on axially loaded grouted piles and to interpret the data in view of predetermining ultimate axial capacity. Design procedures are given that are used by some in the offshore industry to predetermine axial capacity of grouted piles. The influence of stress relief, moisture migration, technical disturbance, and drilling mud on the development of skin friction is discussed. Research studies are discussed which have potential for making significant improvements in the state-of-the-art. INTRODUCTION Axial load pile requirements for offshore drilling/production platforms (typically 1000 to 4000 tons) and/or difficult soil conditions (dense sand, hard clay, reefs, etc.) may preclude conventional pile driving as a viable installation technique for attaining typical design pile penetrations of 200 to 400 ft. When a design embedment cannot be attained, a supplemental installation method is required (31). A supplemental installation method may also be required for sites where calcareous sand deposits predominate. This is because pile driving disturbance can result in low lateral soil pressures which will reduce developable frictional resistance. Methods of grouting a pile into an oversized hole or drilling and under reaming for a cast-in-place pile (Fig. 1) recently have received increased attention by offshore operators. Current technology for computing ultimate capacities of these types of foundation elements is based primarily on experience with drilled-and-undreamed shafts used for land installations. Typical measured ultimate capacities and penetrations of drilled shafts from land installations from which. empirical design parameters are derived are compared in Fig. 2 with typical design ultimate capacities and penetrations required for offshore installations. It shows that as much as a ten-fold extrapolation of the regime of these data must be made for typical offshore design applications. Objectives of this paper are to present a state-of-the-art review of information on design, installation and performance of grouted piles and undreamed footings and to suggest research studies which have potential for making significant improvements in the design and installation of these foundation types for offshore applications. ULTIMATE AXIAL CAPACITY Mathematical Model Ultimate pile capacity is derived from end bearing and from shear stresses developed along the pile shaft. The conventional mathematical expression for ultimate capacity of a cylindrical pile with radius R and penetration L is (regardless of installation method) (Mathematical Equation Available in Full Paper)

Isolation bearings play an important role in the seismic resilience of highway bridges. Flexible and high‐strength reinforcement has been applied in elastomeric isolation bearings to substitute conventional rigid steel plate reinforcement to enhance their lateral performance, for example, lower lateral stiffness and larger deformability. However, the main literature shows that existing flexible reinforcement, such as carbon/glass fiber fabric, may not guarantee a sufficient vertical load‐carrying capacity of elastomeric bearings to meet the design requirement of 30 MPa considering the vertical seismic effect. To this end, the emerging high‐strength steel woven wire mesh was introduced as an alternative flexible reinforcement for the bearings in this study to increase their ultimate compression capacity while maintaining superior lateral performance. Vertical compression tests were conducted on 34 specimens of the proposed unbonded steel‐mesh‐reinforced bearings (USRBs) to investigate the ultimate compression capacity. In addition to the general ultimate behavior of USRBs under vertical loading, the influence of various design parameters (i.e., individual rubber layer thickness, number of reinforcement layers, bearing design load) was investigated through comparisons among the specimens. From the test results, the compressive failure mechanism of USRBs was unveiled, which originated from the tensile failure of the steel mesh reinforcement. The steel mesh reinforcement was proved to increase the bearing ultimate compression capacity to an average of 52.0 MPa compared to fiber‐reinforced bearings, with 85% of specimens exceeding 30 MPa. Moreover, the compression capacity of USRBs was identified to be significantly affected by the individual rubber layer thickness. Specific discussions were further provided concerning the influence of potential manufacturing defects. Finally, suggestions were provided to further enhance the ultimate compression capacity of USRBs based on the results and discussions.

In recent years, cold-formed steel elements have been used more and more as primary load-bearing structures. The development of cost-effective structures is also a main concern in the field of structural engineering. That led to the combination of several materials to achieve this goal. This paper presents an experimental study conducted on cold-formed steel sections with perforations encased in lightweight concrete to investigate their behaviour during subjection to axial compression load. First, the material properties were determined from the tensile coupon test for steel used in cold-formed sections and standard cube/cylinder tests for lightweight concrete. Then, a total of twelve specimens were examined under the axial compression test, with two different cross-sections and various heights. The study's goals are to find out how lightweight encasement affects the behaviour and failure mode of the cold-formed steel column sections. Lightweight concrete encasement has greatly enhanced ultimate axial compression capacity, with a ratio ranging from 74.5–321.1% and 19.5–154.6% based on unit cost. Also, it enhanced the behaviour of cold-formed steel columns, eliminating distortional buckling failure mode and greatly restraining the lateral displacement of both the web and flanges of the cold-formed section. Furthermore, a comparison was conducted between international codes and test results to assess and estimate the behaviour and ultimate compression capacity of perforated bare steel and encased columns subjected to pure axial compression force.

Study on ultimate capacity and design method of cold-formed steel equal lipped angle components under axial compression

Steel-concrete composite adapter for wind turbine hybrid towers: Mechanism and ultimate capacity prediction under compression

Unbonded steel-mesh-reinforced rubber bearings (USRBs) have been proposed as an alternative isolation bearing for small-to-medium-span highway bridges. It replaces the steel plate reinforcement of common unbonded laminated rubber bearings (ULNR) with special steel wire meshes, resulting in improved lateral properties and seismic performance. However, the impact of this novel steel wire mesh reinforcement on the ultimate compression capacity of USRB has not been studied. To this end, theoretical and experimental analysis of the ultimate compression capacity of USRBs were carried out. The closed-form analytical solution of the ultimate compression capacity of USRBs was derived from a simplified USRB model employing elasticity theory. A parametric study was conducted considering the geometric and material properties. Ultimate compression tests were conducted on 19 USRB specimens to further calibrate the analytical solution, considering the influence of the number of reinforcement layers. An efficient solution for USRBs’ ultimate compression capacity was obtained via multilinear regression of the calibrated analytical results. The efficient solution can simplify the estimation of USRBs’ ultimate compression capacity while maintaining the same accuracy as the calibrated solution. Based on the efficient solution, the design process of a USRB with a specific ultimate compression capacity was illustrated.

Exploring key factors affecting the ultimate compression capacity of Unbonded Steel-mesh-reinforced Rubber Bearings

The static tests of nine traditional and bird beak square hollow structure (SHS) T-joints with different s values and connection types under axial compression at brace end were carried out. Experimental test schemes, failure modes of specimens, jack load-vertical displacement curves, jack load-deformation of chord and strain intensity distribution curves of joints were presented. The effects of s and connection types on axial compression property of joints were studied. The results show that the ultimate axial compression capacity of common bird beak SHS T-joints and diamond bird beak SHS T-joints is larger than that of traditional SHS T-joint specimens with big values of s. The ultimate axial compression capacity of diamond bird beak SHS T-joints is larger than that of common bird beak SHS T-joints. As s increases, the increase of the ultimate axial compression capacity of diamond bird beak SHS T-joints over that of common bird beak joints grows. The ultimate axial compression capacity and the initial axial stiffness of all kinds of joints increase as s increases, and the initial axial stiffness of the diamond bird beak SHS T-joints is the largest. The ductilities of common bird beak and diamond bird beak SHS T-joints increase as s increases, but the ductility of the traditional SHS T-joints decreases as s increases.

This paper introduces a trapezoidal orthogonal stiffener steel plate shear wall (TSW). The finite element model of the TSW was developed following the validation of low-cycle repeated tests conducted on a single-span double-layer steel plate shear wall. The paper studies the effects of the flat steel plate thickness, stiffener thickness, stiffener height, and stiffener bottom width on the seismic performance of TSW. Building upon these findings, a theoretical formula for the ultimate shear capacity of TSW was developed. The results prove the following: (1) By changing the flat steel plate thickness, the stiffener thickness, and the stiffener height, the seismic behavior of TSW can be enhanced. It is suggested that the flat steel plate thickness is 4~6 mm, the stiffener thickness is 4~6 mm, and the stiffener height is not more than 60 mm, while the effect of the stiffener bottom width on the seismic behavior of TSW can be neglected. (2) The maximum error is 22.16%, compared to the theoretical value of TSW ultimate shear capacity with the finite element simulation value. However, as the finite element results surpass the test results, it indicates that the formula-derived results are unsafe, necessitating a recommendation for correction.

Axial load capacity and failure mechanism of flange and ring joints of process piping system

In this study, the behavior of screw piles models with continuous helix was studied by conducting laboratory experimental tests on a single screw pile that has several aspect ratios (L/D) under the influence of static axial compression loads. The screw piles were inserted in a soft soil that has a unit weight of 18.72 kN/m3 and moisture content of 30.19%. Also, the soil has a liquid limit of 55% and a plasticity index of 32%. A physical laboratory model was designed to investigate the ultimate compression capacity of the screw pile and measure the generated porewater pressure during the loading process. The bedding soil was prepared according to the field unit weight and moisture content and the failure load was assumed corresponding to a settlement equals 20% of helix diameter. The ultimate compression capacity of screw piles higher than the ultimate capacity of ordinary piles and the ultimate compression capacity increases with decreasing the aspect ratio. The ultimate bearing capacity of the flexible screw pile (L/D<20) is greater than the ordinary pile by 59.5% and with the rigid screw pile (L/D>20), the ultimate bearing capacity could reach 250% compared with the ordinary pile. Also, the estimated ultimate compression capacity of flexible screw piles well agreed with those measured experimentally, but a large difference was noted for rigid screw piles.

Axial compressive behaviours of concrete-filled square GFRP tubular columns at low temperatures

Considering that the pile foundation is widely used in soft soil, in order to improve the prediction accuracy of the vertical ultimate compressive bearing capacity of a single pile, this paper puts forward a calculation model of the pile side friction resistance in homogeneous soil based on the previous research and further deduces the calculation method of pile body internal force in layered soil under the influence of gravity field. In this research, the transmission of load along the pile body is related to the previous research on the ultimate end resistance, and an analytical calculation for the vertical ultimate compressive capacity of a single pile is proposed. The novelty of the method is that the ultimate bearing capacity is solved from the perspective of force transfer while considering its own gravity, making the results more accurate. In order to verify the reliability of the method, four engineering test piles in the soft soil area of Suzhou, China, were selected, and it is indicated that the results of the static load test and finite element simulation are consistent with the proposed method, proving that the method proposed in this paper for predicting the vertical ultimate compressive bearing capacity of single pile in soft soil area has an excellent effect.