Search Results (350)

High-strength steel–ultra-high-performance concrete (UHPC) composite beams provide an efficient solution for lightweight and high-capacity building structures. This study presents a preliminary experimental investigation on the flexural behavior of three high-strength castellated steel–UHPC composite beam configurations employing hinged-bolt shear connectors. This connector type had previously been validated only at the component level and was applied here for the first time in high-strength castellated steel–UHPC composite beams. The three beams were tested under positive bending: a reference specimen with a full-depth cast-in-place UHPC slab and dispersed connectors (CC-DHB), a prefabricated specimen with a C100 precast slab, dispersed connectors, and local UHPC connection regions (PC-DHB), and a prefabricated specimen with a C100 precast slab, grouped connectors, and local UHPC connection regions (PC-GHB). The failure mode, load–deflection response, ductility, interface slip, strain distribution, and flexural resistance were evaluated. The results showed that all specimens exhibited flexure-dominated failure, characterized by the yielding of the steel girder and tensile reinforcement occurring first, followed by concrete crushing near the loading region. A key finding was that, although UHPC was used only in the local connection regions of the two prefabricated configurations, their peak flexural resistances were only 4.5% and 2.5% lower than that of the full-depth cast-in-place UHPC reference beam, indicating that the prefabricated beams substantially reduced UHPC use while retaining nearly the same ultimate flexural resistance as the reference beam. However, their initial stiffness and ductility factors decreased by up to 17%, while their cracking load decreased by approximately 50%. Compared with specimen PC-GHB, the initial stiffness and ductility of specimen PC-DHB increased by approximately 5%. The maximum measured interface slip before the peak load was less than 3 mm for all specimens. A preliminary sectional plastic-resistance method was also developed, and the calculated-to-tested resistance ratios ranged from 1.06 to 1.08. Further validation is required for different connector spacings, web-opening layouts, slab configurations, and shear connection degrees. Full article

Externally bonded carbon fiber-reinforced polymer (CFRP) systems are used to improve the flexural performance of reinforced concrete members. However, premature debonding, particularly intermediate crack-induced (IC) debonding, limits CFRP utilization and may lead to sudden failure. This study experimentally and numerically investigates the effectiveness of CFRP patch anchors with different anchorage configurations in improving the flexural behavior and failure mode of CFRP-strengthened reinforced concrete slabs. Nine reinforced concrete slabs were tested under four-point bending, including one reference slab, two slabs strengthened with longitudinal CFRP strips without anchorage, and six slabs strengthened with CFRP strips and transverse patch anchors. The experimental results showed that CFRP increased the ultimate load by about 30–61% compared with the reference slab. The unanchored specimens failed mainly by IC debonding. In contrast, the patch-anchored specimens showed better strain distribution, delayed debonding, and a shift toward CFRP rupture. The numerical results showed good agreement with the experimental results, with ultimate-load prediction errors below 7%. Changing the patch area did not significantly increase the ultimate load, with about 0.8% difference between the mean capacities of the anchored groups, while end anchors alone were insufficient to prevent debonding. CFRP patch anchors effectively delayed premature debonding and improved CFRP utilization. Full article

To address the challenge of deformation control in operating tunnel structures, this study investigates a novel reinforcement method for operating shield tunnels using a basalt-fiber-reinforced polymer-wrapped concrete-filled steel tube (BFRP-CFST) composite profile. Two primary study variables were considered. At the segment level, the reinforcement condition comprised two levels: unreinforced and BFRP-CFST-reinforced, with three replicate specimens at each level (US-1 to US-3 and RS-1 to RS-3, respectively). At the full-ring level, the number of installed composite profile frames comprised five levels (n = 0, 1, 2, 3, and 4), where n = 0 represented the unreinforced reference condition. A combined experimental and numerical framework was established, including full-scale four-point bending tests on individual tunnel segments and finite element simulations of full-ring linings. Experimental results demonstrate that the ultimate bearing capacity of reinforced segments increased from 534.4 kN to 921.3 kN, corresponding to a 72.4% improvement. The load level before visible cracking increased by 84.2%. At maximum crack widths of 0.2 mm and 2.0 mm, the mid-span displacement of the reinforced segments was reduced by 30.0% and 21.4%, respectively. The test observations indicate that the prefabricated composite profiles effectively delayed crack development and improved the post-cracking stiffness of the segment. Full-ring numerical simulations further showed that installing one to four composite profile frames increased the external load corresponding to a convergence displacement of approximately 10.5 cm by 12.4%, 21.1%, 28.5%, and 37.4%, respectively. Scientifically, the results reveal a staged load-transfer process in which adhesive bonding provides distributed load transfer during the initial response, while mechanical anchors maintain residual load transfer after local interface debonding; they also establish a quantitative relationship between the number of profile frames and full-ring convergence resistance. From an applied engineering perspective, the proposed profile increased the ultimate load and crack-initiation load of the segments by 72.4% and 84.2%, respectively, while its lightweight and prefabricated configuration provides a potentially rapid rehabilitation option for operating shield tunnels. Full article

In order to study the mechanical properties of L-shaped columns of recycled aggregate concrete-filled steel tubes (L-RACFST) with a recycled aggregate concrete (RAC) coarse aggregate replacement rate of 100%, three L-RACFST columns with a RAC coarse aggregate replacement rate of 100% were made to carry out axial compression and two-way bias point load tests. The finite element numerical model was verified on the basis of the test. ANSYS was used to investigate the influence of steel strength, steel thickness, width-to-thickness ratio, and eccentricity on the mechanical properties of L-RACFST columns. Results show that: (1) The eccentricity significantly affects the compressive bearing capacity of L-RACFST columns. Compared with the axial compression specimens, the ultimate bearing capacity of the specimens with eccentricities of 40 mm and 80 mm decreases by 18.67% and 24.84%, respectively. (2) An eccentric load will exacerbate the comprehensive bending deformation of the test specimen. (3) During parameter design, eccentricity has a significant effect on the compressive load-bearing capacity of L-RACFST columns with a 100% RAC replacement ratio. However, increasing the steel’s thickness and strength and reducing the width–thickness ratio can effectively compensate for the loss of compression performance caused by eccentricity. The findings of this study provide guidance for the engineering design and application of steel tube RAC composite special-shaped columns with a high replacement rate. Full article

Steel–concrete composite beams offer significant advantages in long-span, heavy-load, and prefabricated construction; however, the concrete slabs are prone to tensile cracking under negative bending moments. To enhance cracking resistance, uplift-restricted and slip-permitted (URSP) perfobond rib (PBL) connectors were adopted with a cast-in-place high-performance concrete (HPC) topping. Five composite beam-steel column joint specimens were tested under quasi-static cyclic loading. The test variables included connector type, cast-in-place concrete type, and reinforcement grade. In addition, refined numerical simulations were conducted on the test specimens. Both test and numerical results show that: (1) The combined application of URSP-PBL connectors and HPC enhanced the cracking resistance of the composite beam, with the initial cracking load and corresponding cracking displacement increased by approximately 50% compared with the control specimen. (2) The ultimate flexural capacity of the composite beams under negative moments showed limited sensitivity to the type of cast-in-place concrete topping and the reinforcement grade within the tested range. (3) The use of URSP-PBL connectors improved the flexural stiffness of the composite beams. (4) The URSP-PBL specimens showed good energy dissipation capacity under cyclic loading, which was further improved with the addition of HPC in the topping. Within the tested range, the reinforcement grade showed limited influence on this performance. This study provides a scientific basis for the crack control design and engineering application of long-span composite beams. Full article

Functionally graded concrete (FGC) is an advanced building technique that allows structural components to satisfy diverse mechanical and durability specifications. In this study, hybrid geopolymer concrete (HGC) was used in constructing reinforced FGC beams to improve their flexural performance and sustainability. One HGC mix was used and compared with the corresponding control cement-based concrete mixture. The HGC mix was made of FA, slag, and dolomite powder (DP) binders. The structural performance of ten reinforced FGC beams, with different cross-sections and varying concrete layer configurations, was evaluated by four-point bending tests. The results indicated that beams utilizing HGC in the tensile zone showed improved ductility and load-carrying capacity relative to those constructed with the corresponding cement-based concrete. The functionally graded configuration, particularly when HGC is placed in the crucial tension zone, markedly enhanced both the ultimate deflection by 30% and ductility by 73%. These findings highlighted the advantages of using HGC in constructing FGC beams for sustainable, high-performance concrete structures, facilitating diminished cement usage, reduced carbon emissions, and enhanced structural resilience. Full article

This paper presents a methodology to evaluate the entire process of thermal evolution and fracture failure within stay cables subjected to sheath fires. Computer software FDS 2021 and ABAQUS 2021 are applied to build a sequentially thermos–mechanics coupled method integrating thermal, structural, and fracture dynamic analyses in stay cables under sheath fire exposure conditions. Herein, three representative fire scenarios including full-circumferential, top-side, and bottom-side ignition are reconstructed. Further, 127 individual wires, accounting for interstitial cavity radiation and contact heat transfer, are utilized to perform analysis on sectional temperature in stay cables. The results indicate that the ignition mode dictates the cross-sectional temperature gradient, with localized ignitions inducing highly asymmetric thermal fields and pronounced internal bending moments. Elevated temperatures trigger a progressive load redistribution from the degraded fire-facing wires to cooler internal layers. Ultimately, abrupt global fracture occurs when the residual ultimate load-carrying capacity intersects with the actual applied tension, resulting in a fracture morphology that closely corresponds to the spatial thermal distribution. Furthermore, the structural capacity degradation exhibits three distinct time-dependent stages: a slow degradation stage, a sharp decline stage, and a recovery stage. Among the analyzed scenarios, full-circumferential ignition induces the most drastic overall capacity reduction, while bottom-side ignition poses a markedly greater rupture risk than top-side ignition. Full article

The layer-wise deposition process of three-dimensional concrete printing (3DPC) induces anisotropic behaviour, while cementitious materials exhibit pronounced tension–compression strength asymmetry. This study develops a concurrent topology and printing-direction optimisation framework for plain 3DPC under Drucker–Prager (D–P) strength constraints. Within a solid isotropic material with penalisation (SIMP) formulation, material density and printing orientation are updated simultaneously using the Method of Moving Asymptotes (MMA). A double-angle vector-field mapping regularises the π-periodic orientation field, while element-wise D–P failure indices are aggregated into a differentiable global constraint through P-norm aggregation with adaptive scale correction. Numerical studies on a four-corner pinned plate, a T-shaped bracket and a perforated deep beam show that the strength constraint reshapes load paths, suppresses local strength violations and increases ultimate load capacity by approximately 200%, 176% and 42%, respectively, relative to compliance-based optimisation. The optimised deep-beam layouts are reconstructed, converted into continuous printing paths, fabricated and tested under three-point bending. Experimentally, the mean ultimate load increases from 8.13 to 9.54 kN, corresponding to an increase of 17.39%, while the mean displacement at peak load and pre-peak energy are 20.58% and 41.16% higher, respectively. The experimental and finite element comparisons show closely similar ultimate-load increases of 17.39% and 17.43%, respectively. The framework provides a strength-aware route from concurrent numerical optimisation to the fabrication and structural assessment of plain 3DPC components. Full article

Prefabricated pile-cap joints have been applied in concrete pile foundations in waterway revetment structures for decades. However, the mechanical performance of such joints for small-section (≤400 mm) prestressed piles has not been systematically validated, which hinders their application in civil and waterway engineering. This study evaluates this joint system through full-scale tests on six identical 400 mm × 400 mm prestressed concrete pile-cap specimens (C60 pile, C30 joint concrete, HRB400 anchoring bars threaded into embedded steel sleeves) under monotonic tension, bending, and shear, with strain gauges monitoring the response. The results show that the joint sustained a tensile load of 1400 kN, which exceeds the pile’s design value by 52%, a bending moment of 277 kN·m, which is 32% higher than the pile’s ultimate capacity, and a shear force of 680 kN, which reaches more than 2.5 times the design shear, without any occurrence of joint failure. These findings provide the first comprehensive experimental evidence that this prefabricated joint system can effectively transfer tensile, bending, and shear loads in small-section prestressed piles, thereby supporting its safe application in green, industrialized engineering. Full article

To improve the bending resistance and support the domestic development of deepwater subsea wellhead equipment, a three-dimensional finite element model (FEM) of the SXW-15 subsea wellhead system was established in ANSYS Workbench considering contact nonlinearity and rigid-locking mechanisms. Based on representative deepwater drilling and completion conditions, the effects of the friction coefficient, locking preload, blowout preventer (BOP)/lower marine riser package (LMRP) top load, casing hanger internal pressure, and tubing load on the ultimate bending capacity of the system were systematically investigated. The results show that the bending capacity increases with increasing friction coefficient and locking preload, whereas it decreases with increasing top load and tubing weight. The internal pressure of the casing hanger exhibits a pronounced nonlinear influence on the bending resistance, and the maximum bending capacity occurs at an internal pressure of approximately 4000 psi. Based on the mechanical analysis, several innovative designs were proposed, including a layered load-bearing structure, a gravity-set metal sealing assembly, a self-supporting rigid-locking mechanism, and an integrated multifunctional tool system, aiming to improve load-transfer efficiency, connection stiffness, and high-pressure sealing stability. Land-based testing and offshore field applications were subsequently conducted to verify the engineering applicability of the system. The subsea wellhead system with innovative designs maintained satisfactory structural integrity and sealing reliability under conditions of 15,000 psi internal pressure and 12.7 million lb axial load. Good agreement was obtained between finite element predictions and field test results. The present study provides theoretical support and guidance for the structural designs and engineering applications of deepwater subsea wellhead systems. Full article

This study introduces a novel prestressed precast hollow-core slab system with integrated polystyrene foam inserts and a spliced design utilizing cast-in-place wet joints, aiming to resolve the inherent trade-off between self-weight reduction and load-bearing capacity in precast floor systems. An experimental investigation was conducted on three individual slabs with varied foam geometries and four jointed slabs with different foam configurations and joint concrete types. All specimens were tested under four-point bending. The experimental program meticulously assessed failure modes, load–displacement characteristics, and load–strain relationships of the proposed slab systems. Results reveal that the hollow-core slabs exhibited failure mechanisms similar to conventional cast-in-place slabs, with cracking initiating in the pure bending region and then propagating along the slab edges. Specifically, specimens with square and circular foam inserts achieved weight reduction rates of 24.57% and 19.78%, respectively. Concurrently, their ultimate loads increased by 32.39% and 46.46% compared to the cast-in-place control. The prestressing tendons remained elastic at ultimate load, confirming that failure was governed by concrete crushing in the compression zone rather than tendon rupture, which represents a ductile failure mode providing sufficient warning prior to collapse. For the jointed specimens, while cracks fully penetrated the foam inserts in the pure bending zone, no cracking occurred at the wet joint interfaces, signifying robust composite action. The load capacity of these jointed specimens surpassed that of the equivalent cast-in-place slab by 19.1% to 50.7%. Based on an evaluation of material cost, structural efficiency, and flexural performance among the tested configurations, the combination of square foam inserts and conventional C40 concrete in the wet joint is recommended. This research provides a critical experimental foundation for the development of lightweight, high-performance precast floor systems in prefabricated concrete construction. Full article

This paper presents the results of experimental investigations of the flexural capacity of the main beams in a storage platform with plan dimensions of 5.0 m × 2.0 m. The platform was designed as a grid structure, with main beams made of cold-formed channel sections and crossbeams made of sigma-section members. The crossbeams, spaced at 0.6 m, were connected to the main beams using M12 bolts and angle cleats. Eight test specimens were examined, with section heights ranging from 250 to 500 mm and wall thicknesses of 3 or 4 mm, fabricated from S350GD+Z steel. Loading was applied in a four-point bending scheme until failure of one of the main beams, while recording the moment–deflection relationship. The obtained failure loads were compared with the design resistances calculated in accordance with EN 1993-1-3. Additionally, GMNIA analyses were performed for the tested storage-platform structures using the Idea StatiCa Member version 24.1 software, incorporating measured material properties and equivalent geometric imperfections in accordance with prEN 1993-1-14. The adopted procedure included a sensitivity study to investigate the influence of different combinations of local and distortional buckling mode imperfections on the numerical results. The observed behaviour was characterized by interaction between distortional and local buckling modes, accompanied by yielding in the compression zone. The GMNIA analyses predicted the ultimate bending resistance with good accuracy, yielding FEM-to-test resistance ratios between 0.93 and 0.98. The sensitivity study indicated that the predicted ultimate resistance was only weakly affected by the assumed combination of local and distortional imperfection modes. For the investigated platform systems, the effective section approach according to Eurocode 3 provided accurate predictions of the ultimate resistance, with calculated-to-test resistance ratios ranging from 0.96 to 1.01. This agreement is discussed in the context of the possible stiffening effect of crossbeam-to-web connections. Full article

Fiber-reinforced concrete is increasingly used to improve the mechanical and structural performance of reinforced concrete elements. This study presents a comparative experimental investigation of reinforced concrete beams incorporating steel and polypropylene fibers. Seven beams were examined, including a reference concrete and fiber-reinforced concrete mixtures containing 1.0%, 1.5%, and 2.0% fiber volume fractions. The experimental program included compressive strength tests on 21 cube specimens, shrinkage measurements on 21 prism specimens, and bending tests on reinforced concrete beams. The properties studied included compressive strength, shrinkage strain, ultimate load capacity, load–deflection response, crack initiation, crack width, and post-cracking behavior. Polypropylene fibers provided the greatest crack-control benefit, reducing shrinkage strain and maximum crack width by up to 50% and 93%, respectively, compared with the reference concrete. Steel-fiber-reinforced beams achieved the highest ultimate load, with an increase of up to 22% relative to the reference beam, and showed higher calculated displacement ductility indices. The results indicate that, under the tested conditions, steel fibers were more effective in improving load-carrying capacity and displacement ductility, whereas polypropylene fibers were more effective in controlling shrinkage and crack development. These findings support fiber selection according to the required balance between load capacity, deformation response, crack control, and serviceability. Full article

This study investigates the behaviour of normal-strength concrete (NSC)–ultra-high-performance concrete (UHPC) composite slabs under four-point bending through experimental tests, finite element simulations, and analytical modelling. A total of 12 slabs were tested under static loading to examine the effects of UHPC layer position, UHPC thickness, reinforcement ratio in the UHPC layer, and shear span ratio on load-deflection behaviour, crack development, strain evolution, and failure mode. The test results showed that, when UHPC was placed in the tension zone, the slabs generally exhibited higher post-cracking stiffness and load capacity. The specimens with the longitudinal reinforcement spacing in the UHPC layer reduced from 100 mm to 50 mm exhibited an approximately 16% increase in ultimate load, but they were more prone to develop localised cracks and shear failure with a high reinforcement ratio in the UHPC layer and a small shear span ratio. When UHPC was placed in the compression zone, the specimens showed greater deformation capacities. With the same UHPC thickness, reinforcement ratio, and shear span ratio, their failure deflections were approximately 1.5–4.8 times those of the corresponding specimens with UHPC in the tension zone, whereas their failure was mainly governed by interface debonding. Finite element models were also developed and validated against the test results, followed by parametric analyses. The numerical results indicate that interface bond strength plays a dominant role in failure mode and deformation capacity, particularly for slabs with UHPC cast in the compression zone. Increasing the UHPC thickness generally improves the stiffness and load capacity, whereas insufficient thickness increases the risk of shear failure or interface debonding. Finally, an analytical model was proposed for composite slabs with different UHPC layer positions, and the model was shown to provide a reasonable prediction of the load-deflection curve of flexure-dominated slabs. Full article

With the increasing construction of pile foundations on mountain slopes, the asymmetric stress field induced by slopes significantly reduces the lateral soil resistance of piles. Most existing studies focus on piles located at slope crests, and there is an obvious gap in p-y curve calculation methods for piles embedded in clay slopes. In this study, model tests of single piles in clay slopes with slope angles of 0°, 15°, and 30° are carried out. The test results reveal that the increase in slope angle aggravates the horizontal displacement and bending moment of piles and moves the pile rotation point downward. Numerical model is adopted to extract p-y curves at various embedded depths and slope angles. It is found that rising slope angles continuously degrade the initial stiffness and ultimate soil resistance of p-y curves, and such degradation weakens with increasing embedment depth. The core innovation of this paper is establishment of a modified p-y curve model considering slope effects. A simplified analytical method for slope piles is further proposed based on the load transfer method. The prediction errors of this modified model are within the allowable engineering range, which can provide a reliable analytical tool for calculating the lateral bearing capacity of pile foundations in clay slopes. Full article