U-shaped Steel Research Articles

Study on the deformation failure mechanism and coupling support technology of soft rock roadways in strong wind oxidation zones

Due to the influence of sedimentary environment, the coal seams and overlying rocks in the wind oxidation zone exhibit developed fractures, high rock porosity, strength attenuation, and poor self-stability. It leads to the large deformation of the surrounding rock and managing the roof of roadways difficultly. This made the roadway excavation extremely difficult. And the rendering conventional “bolt-cable-mesh (belt)-shotcrete” combined support system was not applicable. In this paper, the No. 49,104 air return roadway in the strong wind oxidation zone of the Shuiquan Coal Mine was selected as the engineering background. The change trends of the coal and rock in the strong wind oxidation zone physical and mechanical properties were revealed, and the deformation and failure mechanism was analyzed. According to the deformation and failure characteristics of the roadway in the wind oxidation surrounding rock with engineering practice, a coupling support scheme “pregrouting + anchor net and sprayed concrete + inverted arch structure + U-shaped steel + high and low-pressure, deep and shallow-hole reinforcement grouting” was proposed. A roadway grouting reinforcement diffusion range model was established in COMSOL Multiphysics, and the grouting diffusion range was then imported into FLAC3D to compare and analyze the coupling support scheme reinforcement effect of roadway in the strong wind oxidation zone. And the coupling support scheme was used to reinforce the No. 49,104 air return roadway, and the reinforcement effect was monitored in situ. Results showed that the proposed coupling support and reinforcement scheme can be employed to effectively control the deformation of the surrounding rock and the expansion of plastic zone damage. And the stability and safety of the roadway were significantly improved. This coupling support scheme was reasonably designed, and it could provide an engineering reference for the support and reinforcement of roadways in weak and crushed surrounding rocks under similar geological conditions.

Flexural study on U-shaped steel–concrete composite beam cross joints with L-shaped connection longitudinal transition components

The paper focuses on the U-shaped steel–concrete composite bottom beam cross joints of U-shaped Steel-concrete Composite Open-web Sandwich Plate (USCOSP), presenting a new type of cross joints transmitting the internal force of steel web by L-shaped connection Longitudinal Transition Component (LLTC). LLTC consists of sleeves, L-shaped connection plates and threaded rebars installed on the steel web using sleeves and L-shaped connection plates. Compared with the conventional cross joints which transmit internal force of steel web by Welded Longitudinal Transition Rebar (WLTR), the LLTC cross joints transfer eccentric internal force within the steel web. Through simple-point loading experiments with simply-supported at four ends, the research experimentally investigated the flexural behavior of the WLTR cross joints and the LLTC cross joints. The five specimens were varied to differ in the type of longitudinal transition components, the diameter of WLTR, the number of threaded rebars of LLTC and the strength grades of threaded rebars of LLTC. Experimental results showed that the failure mode of U-shaped steel–concrete cross joint was the buckling of steel web, the buckling of top longitudinal rebar and crush on the concrete under compression near the central region. The LLTC cross joints experienced higher load capacity and better ductility than WLTR cross joints because of little steel web buckling. The ultimate load capacity calculated according to JGJ 138–2016 and the deflection in the elastic stage calculated according to the displacement method agree well with the experiment results.

Fire-resistant test and fire protection layer research of U-shaped steel–concrete composite beams

Four U-shaped steel–concrete composite beams with channel connectors (CUSCB) were designed and tested under the ISO-834 standard fire curve and distributed vertical load. The research parameters included the fire protection layer thickness, the fire-resistance reinforcement in the U-shaped steel and the load ratio. The temperature distribution, fire resistance, and failure modes of the CUSCB specimen were investigated. The fire tests indicated that the failure mode of the specimen is flexural damage, the connection interface between the flange and web of composite beam remains intact. And the local buckling phenomenon did not happen on U-shaped steel. The fire resistance increased with the decrease of load ratio, and the configuration of fire protection layer and fire-resistance reinforcement. Then the numerical simulation was conducted to research the fire performance of CUSCB, and the simulation results of the temperature field and fire resistance were in good agreement with the test results. Moreover, a flexural bearing capacity calculation method for the U-shaped steel and concrete composite beam under standard temperature rise curve is proposed, which can be applied to calculate fire resistance. Finally, the calculation tables for the thickness of fire protection layer are proposed based on the delaying temperature mechanism.

Study on Failure Mechanism and Zoning Control of Weakly Cemented Roadway Adjacent Chambers

The strength of weakly cemented surrounding rock is low, and the bonding ability is weak. The rock forming roadway is affected by the stress disturbance after the excavation and support of adjacent chambers, which can lead to problems such as large deformation of the surrounding rock and significant differences in deformation areas. Through comprehensive theoretical analysis, on-site measurement, and numerical simulation, the distribution and evolution characteristics of stress in the surrounding rock adjacent chambers were studied. The results of this study indicated that, the surrounding rock stress crosses the adjacent chambers and forms a concentrated area near the weakly cemented roadway, and that the stress increase ratio of surrounding rock within the stress concentration range can reach 50%. A longer distance of the chambers from the weakly cemented roadway corresponds to a smaller surrounding rock stress concentration area. When the distance exceeds approximately 12 times the average height of the chambers, the surrounding rock stress concentration tends to disappear. According to the support concept of “allowable deformation” + “released pressure” + “restricted shape”, control countermeasures for surrounding rock at different levels are given, which are dominated by U-shaped steel + flexible material and are effective for controlling roadway deformation.

Seesaw-arm energy dissipation system with U-shaped steel dampers

This paper presents an investigation of the extended seesaw system using a seesaw-arm member with U-shaped steel dampers for improving the seismic energy dissipation in building structures. One of the notable features of the existing seesaw system is its usage of a quasi-linear motion mechanism, which allows the bracing members to remain tensile during vibration. In addition, a seesaw-arm concept is proposed for magnifying the damper deformation. Evaluation methods for the lateral stiffness and strength of the proposed system were derived. Then, cyclic loading tests were performed on six specimens, revealing that the proposed system has a stable hysteretic property and large energy-dissipation capacity. The accuracy of the stiffness and strength evaluation was assessed through comparisons with the test results. The evaluation of the displacement amplification factor of the damping system agreed well with the test results. Seismic-response analyses of five-story steel frame models adopting the proposed system were conducted. The maximum story drift angle, time-history responses of displacement and energy, and plastic-hinge formation were compared with those of the bare frame model. The analysis results revealed the efficiency of the proposed system for reducing seismic responses. Furthermore, a larger shape factor of the seesaw-arm member corresponded to better seismic performance.

Study of U-shape steel-encased composite beams with variable sections under negative bending moments

To reduce steel consumption and improve the negative moment bearing capacity of composite beams, a new type of composite beam with an external U-shaped steel plate was proposed in this paper. Static load tests of three scaled simply supported composite beams were completed, and the failure patterns, load–displacement curves, strain distributions, and slip of the new composite beams under negative bending moments were researched. The results showed that the new composite beam under negative bending moments underwent typical flexural failure with excellent ductility (ductility coefficient of 6.2), wherein the embedded steel plate played a key role in the loading process of the composite beams, contributing more than 50% of the flexural load capacity. On the basis of the experiments, finite element models were established in ABAQUS to investigate the influence of different construction parameters, including the material strength, thicknesses of the external steel plate and the embedded steel plate, and reinforcement ratio. Finally, design formulas were derived according to the simplified plasticity theory to calculate the flexural capacity of the proposed composite beam for engineering practice, which achieved close agreement with the experiments, with an average relative error of 3.5%.

An Experimental Study on Plate Splicing of Prefabricated Plate Foundation

Tower foundations are generally of a cast-in-place structure with the disadvantages of low industrialization level and long construction period. The development of prefabricated foundation for transmission line projects is efficient to improve the industrialization level of the construction of tower foundation. In this study, the schemes of post-pouring belt U-shaped steel connection, post-pouring belt lap connection, grouting sleeve connection, and post-tensioned bond prestressed reinforcement connection, which have been widely used on building structures, are newly proposed to apply on plate foundation. The schemes were compared on processing, transporting, on-site constructing and performance. The pseudo-static tests on cast-in-place plate strip, post-pouring belt U-shaped steel connection and post-pouring belt lap connection plate strip were carried out. The results revealed that all the test plate bands were damaged in the bending mode, same as that of ordinary concrete. When U-shaped steel is adopted, more than 90% of the cast-in-place bearing capacity can be reached. The initial stiffness of prefabricated plate strip and cast-in-place strip is basically the same. The load-bearing capacity of the component is relevant to the anchorage length of the U-shaped steel. Although increasing the concrete strength of post-cast belt can improve the ultimate bearing capacity and shorten the construction period, the deformation capacity is reduced. Compared to other connection methods, post-pouring belt U-shaped steel connections have the advantage of simple construction, higher bearing capacity and stability. In summary, the post-pouring belt U-shaped steel connection scheme is recommended.

Experimental Investigation on Deformation Characteristics of Strutted U-Shape Sheet Pile Flexible Retaining Structures in Excavations Using 3D Printing

U-shape steel sheet piles are widely used in deep and large excavation engineering due to their excellent soil-retaining and water-stopping performances. To achieve deformation control in excavations, an experimental investigation on the deformation characteristics of a strutted U-shape sheet pile flexible retaining structure was conducted. Single-layer and double-layer strutted retaining structure excavation indoor model tests in sand, where U-shape sheet piles were formed by 3D printing, were successfully accomplished. Deformation was monitored in real time during the test. The results show that the lateral displacement mode of the retaining structure transformed with the change in excavation from the “cantilever” to the “bulge” and finally developed into an intricate “recurve bow”. The average maximum lateral displacement was 0.756% of the excavation depth. With a maximum settlement of 0.375% of the excavation depth on average, the distribution of ground settlement behind walls changed from “exponential” to “triangular” before ultimately transforming into “trough” or “trapezoid” mode. The maximum settlement to maximum lateral displacement ratio (smax/δmax) on average was 0.54; the maximum settlement deformation rate was always less than the maximum lateral displacement deformation rate.

Flexural behavior of large-scale U-shaped steel-concrete infilled composite beams with flat and embossed webs

Most popular shape of steel-composite beams is the exposed type in which wide-flange steel sections are connected to the reinforced concrete (RC) slab through shear connectors. However, recently innovative U-shaped steel–concrete infilled type composite beam sections are introduced which demonstrated promising structural performance. In these composite beams, the U-shaped steel section filled with concrete serves as formwork in fresh state of concrete while it behaves as main reinforcement during the service life of the structures. Although, active research has been conducted on former type, but research on the later infilled type beams seems insufficient. There exist several research questions which need to be addressed for optimized and efficient design of these innovative composite sections. In this paper, six large-scale U-shaped steel–concrete infilled composite beams with flat and embossed webs were tested to investigate their flexural behavior. The tested composite beams were designed with angle shear connectors which provide efficient shear transfer mechanism with economy. The main parameters of the tests were the shape of web and the spacing of the shear connectors. The effects of embossed web on horizontal shear transfer and its contribution to the flexural capacity were mainly focused. In addition, a detailed section analysis was conducted to comprehend the experimental observations.

Sliding U-shaped steel damper for multi-directional displacement

A U-shaped steel damper may undergo multi-directional displacements. However, U-shaped energy-dissipation plates with large width-to-thickness ratio may experience unexpected torsional deformation during an out-of-plane displacement and provide an unstable restoring force and energy dissipation. Discussed here is a sliding U-shaped steel damper that uses connecting structures to obtain force-free sliding in out-of-plane directions. Cyclic performances under multi-directional displacements were verified experimentally, and out-of-plane force-free sliding was observed. The energy-dissipation plates only exhibited in-plane plastic deformation and provided a stable restoring force as well as energy dissipation. Equations for the yield and ultimate restoring forces were developed by considering the loading angle, and a finite element model in ABAQUS reproduced physical tests. Connection structures were thus improved for higher stiffness, and lateral sliding that considered the peak vertical force was also proposed. Finally, an analytical hysteretic model for the sliding U-shaped steel damper was abstracted based on the test and simulation results, which shows acceptable agreement with the test results.

Stability analysis and deformation control method of swelling soft rock roadway adjacent to chambers

The surrounding rock of swelling soft rock roadway has high clay mineral content, strong expansibility after encountering water, low strength and poor cementation. The roadway is prone to large deformation under the influence of complex geostress. Combined with the support change of the development roadway of 2# coal in Hongqingliang mine, through geological survey, field observation and indoor test, the failure mechanism of the traditional support method of “anchor bolt + anchor cable + anchor mesh + shotcrete” was revealed by the adjustment of the surrounding rock stress after the excavation and support of the adjacent chambers. The research results show that the surrounding rock stress will cross the adjacent chambers and form a concentrated area near the weakly cemented roadway, and the maximum stress increase ratio of surrounding rock within the stress concentration range will reach 50%. The farther the chambers are from the weakly cemented roadway, the smaller the range of the surrounding rock stress concentration area. When the distance exceeds about 12 times the average height of the chambers, the surrounding rock stress concentration tends to disappear. Based on the fully enclosed combined support method of the "U-shaped steel sheds closure roof and sides + filling flexible material behind the sheds + laying reinforcement mesh and concrete in floor + strengthening key parts", the construction process flow applicable to the working condition of swelling soft rock roadway is formulated.

Experimental Investigation on Flexural Behavior of U-Shaped Steel–Concrete Composite Beams with Bolt Connections under a Negative Bending Moment

Because U-shaped steel beams filled with concrete have the advantages of reduced construction period and superior structural performance, they have been widely used as structural elements. In this study, the flexural behavior of newly developed bolt-connected U-shaped steel and concrete composite beams under a negative bending moment was experimentally evaluated. The main test variables were bolt spacing in bottom steel plates and types of U-shaped steel sections. Test results showed that the flexural behavior of the composite beams is determined by the plate-buckling mode of bolt-connected bottom steel plates. Composite beams with a greater bolt spacing than that in the standard AISI S100-16 experienced early plate buckling of the bottom steel plates, resulting in reduction of flexural stiffness and maximum flexural strength. Thus, the buckling mode of bolt-connected bottom plates should be considered for bolt-connected U-shaped composite beams under a negative bending moment. The longitudinal lips of U-shaped steel sections can increase the flexural performance of composite beams due to anchorage performance of the steel sections with lips.

Flexural behavior of U-shaped steel-concrete composite beams under positive bending

The use of cold-formed U-shaped steel and concrete composite beams has increased with the advantage of permanent steel form as a load-resisting element. In this study, a new type of U-shaped steel-concrete composite beam with a bolt connection was proposed. Four-point flexural tests of full-scale specimens were performed to evaluate the flexural behavior of the composite beams under a positive bending moment. The main test parameters were the types of U-shaped steel sections and location of the neutral axis at ultimate strength. The U-shaped composite beams under positive bending behaved similarly to the composite beams with an I-shaped steel section. The strain compatibility method is recommended to evaluate the positive flexural strength of the composite beams. In addition, the effective flexural rigidity was proposed to capture the increasing trend of the flexural stiffness ratio according to the shear span-to-depth ratio.

Study on Stress Disturbed Mechanism and Supporting Method of Weakly Cemented Roadway near Chambers

After excavation of the weakly cemented roadway adjacent to the chambers, deformation characteristics such as roof subsidence, roadway extrusion, and floor heave appear, showing the characteristics of large deformation of surrounding rock, long deformation duration, and serious damage, which are not conducive to guaranteeing safety mining. Based on the technical means of the rock mechanical property test, mineral composition analysis, in situ stress test, and surrounding rock deformation monitoring of 2# coal roadway in Hongqingliang coal mine, a numerical simulation study on the influence of surrounding rock stress on adjacent chamber groups was carried out. The physical and mechanical properties of the weakly cemented rock were obtained, the stress distribution law of the 2# coal roadway was mastered, the deformation characteristics of the surrounding rock of the weakly cemented roadway were obtained, and the deformation and failure mechanism of the weakly cemented roadway adjacent to the chambers were revealed. The relationship between the regional stress increment of the chambers and the failure range of the surrounding rock of the roadway is revealed, establishing a mechanical model of allowable deformation + stress release + controlled form with U-shaped steel as the main structure. The roadway support countermeasures were given and applied in engineering practice.

Theoretical calculation method for critical buckling load of locally stiffened U-shaped steel sheet pile using the dynamic coordination coefficient method

In order to solve the problem that U-shaped steel sheet piles (USSSPs) are prone to buckling when inserted, we propose a local stiffened U-shaped steel sheet pile destabilization critical load calculation method, namely ‘dynamic alignment coefficient method’, and analyze the influence of stiffening area, stiffening position and number of stiffening plates on the stiffening effect.The study shows that when the total stiffening area is certain, there is a scheme of stiffening plate arrangement to maximize the critical load value of USSSPs with determined length,and reveals the law of local instability caused by the small width of single stiffening plate when the number of blocks is too large. The critical load value of the member can be increased by 13.55% with the variation of the single stiffener plate arrangement position for 10 m long USSSPs, and the optimized theoretical scheme of stiffener plate arrangement for 10 m and 30 m long USSSPs with different total stiffener area is obtained.

Seismic behavior and theoretical analysis of mortise–tenon joints reinforced with steel components

Wood structures have been vigorously popularized and developed because they have low carbon emissions and acceptable earthquake resistance. To solve the general pull-out failure of mortise–tenon joints (MTJs) under earthquake loads, reinforcement techniques, such as steel strip plate (SSP), hollow rectangular steel plate (HRSP), U-shape steel plate (USP), and T-shape steel plate (TSP) methods, have been proposed. Low cyclic loading tests were conducted on five joints to investigate the effect of reinforcement methods on the seismic behavior of MTJs. Furthermore, the peak bearing capacity of reinforced MTJs was theoretically analyzed based on European, American, and Chinese specifications; the calculations were compared with the test results. To verify the accuracy of the theoretical analysis, ABAQUS software, a finite element simulation application, was used. The test results show that the failure modes of joints with or without reinforcements are tenon pull-out, self-tapping screw pull-out, and shear failure. Moreover, the USP-reinforced MTJ exhibited the best seismic performance, followed by the MTJs reinforced with TSP, HRSP, and SSP. The theoretical calculation and test results are in good agreement. The simulation results indicate that the proposed calculation methods can accurately predict the peak bearing capacity of steel-reinforced MTJs.

Comparative study on the seismic behaviour of assembled composite walls with vertical joint rigid connections and ductility connections

To investigate the efficient dry connection type of fully assembled composite (FAC) walls, two novel vertical joint connection types, including rigid connections (box connections) and ductile connections (U-shaped plate connections), are proposed. In the experiment, three specimens were constructed and tested under in-plane reversed cyclic loading, including specimens with box connections (FAC-B) and U-shaped steel plate connections (FAC-U) and a specimen with a horizontal cast-in-place assembled composite (CAC) wall as the reference specimen. In the reversed cyclic loading test, the failure mode, hysteretic behaviour, bearing capacity, stiffness degradation and energy dissipation capacity were obtained. The test results indicated that the failure mode of all specimens was shear failure. In addition, a finite element model (FEM) of FAC-U is subsequently established and validated to further investigate the seismic performance of the plate thickness, concrete strength, compression ratio and block strength on the bearing capacity and ultimate displacement.

Experimental research on fire performance of U-shaped steel-concrete composite beam under uniformly distributed loading

Four U-shaped steel-concrete composite beams with channel connectors (CUSCBs) were designed and tested under the uniformly distributed vertical load and ISO-834 standard fire condition. The sectional temperature distribution, mid-span deformation development, fire resistance, and failure modes of each CUSCB under fire were investigated. The test results reveal the following facts: (1) All specimens fail flexurally; (2) The interface between the concrete flange and the U-shaped steel web remain intact and no local buckling occurs in U-shaped steel; (3) The concrete temperature decreases from the fired surface to the non-fired surface gradually; and (4) The temperature of the concrete at the corner between the lower flange and the web of U-shaped steel is higher than the concrete within the beam. Moreover, the fire resistance increases with the increase of fire protection layer thickness; and the bottom reinforcement in U-shaped steel can improve the fire resistance. The fire behavior of CUSCBs was also analyzed using the finite element program ABAQUS and the simulated temperature distributions and fire resistances were found to be in good agreement with the test results. Furthermore, the parametric analysis results show that the thickness of fire protection layer, the diameter of bottom reinforcement, the load ratio, and the thickness of U-shaped steel have significant impact on the fire resistance, while the section size and material strength have little impact. Lastly, design suggestions for the fire resistance design of CUSCBs are proposed.

Study on Seismic Behavior of Spliced Outer Sleeve Beam–Column Joints with U-Shaped Steel Plates

Study on Seismic Behavior of Spliced Outer Sleeve Beam–Column Joints with U-Shaped Steel Plates

Overall stability capacity design of T-shaped irregularly concrete-filled steel tube columns considering axial compression and any directional moments

A slender T-shaped irregularly concrete-filled steel tube column (T-ICFSTC) may be subjected to overall instability failure under combined axial load and moment. But current research is not available about a complete design of T-ICFSTCs subjected to axial compression and any direction bending moments because of a complicated parameter study involved in the analysis. This paper investigates the overall stability capacity performance and design prediction of the T-ICFSTCs that are formed by I-shaped steel, U-shaped steel and several cell infilled concrete. First, the finite element model for analyzing the overall instability performance and failure is established and verified by the previously experimental tests carried out by the authours. Then, the overall stability capacity of T-ICFSTC around its symmetric axis is investigated numerically and accordingly design formulas of φy-λny are established. In particular, interaction influence between initial imperfection direction and applied bending moment direction is studied, thus resulting in a critical initial imperfection direction relatively to applied bending direction. Sequently, the load-bearing capacity and performance under any direction bending moments are explored numerically and the normalized design curves reflecting interaction of N-M and Mx-My at their limit states are formulated by fitting the FE results of examples. Finally, a complete set of overall stability prediction formulas of T-ICFSTCs under combined axial load and any directional bending moment are established and the results obtained agree well with FE numerical investigation results.