Yield Load Research Articles

Multi-Criteria Optimization of Wind Turbines in an Offshore Wind Farm with Monopile Foundation Considering Structural Integrity and Energy Generation

Offshore wind energy plays a crucial role in achieving renewable energy targets, with OWFs facing unique environmental challenges that impact turbine performance and structural demands. This study develops an advanced optimization methodology to identify the most effective layout configurations for offshore wind farms (OWFs) with monopile foundations, focusing on enhancing structural integrity and energy generation efficiency. Using a multi-criteria optimization approach, the effects of wind turbine spacing, angular orientation, and height on energy yield and monopile loading were evaluated. Based on a seven-year dataset from the Ouido site in South Korea, where the mean wind speed is 6.95 m/s at a 150 m hub height, optimized configurations were determined. For average wind conditions, a turbine spacing of 250 m, a hub height of 148 m, and an orientation angle of 36.87° minimized wake losses and distributed structural loads effectively. Under rated wind speeds of 10.59 m/s, a spacing of 282 m, a hub height of 155 m, and an orientation angle of 45° further enhanced performance. These designs reduced wake interference by 25%, decreased monopile fatigue loads by 18%, and lowered the levelized cost of electricity (LCOE) by up to 15%. This study’s findings provide a robust framework for optimizing OWFs to increase energy yield, improve operational efficiency, and ensure economic viability.

Comparing numerical simulation methods for evaluating hysteretic response of self-centering shear walls reinforced with SMA-ECC under cyclic loading

Under the action of earthquake, the traditional shear wall structure has the problems of excessive residual deformation and macroscopic cracks. The SMA-ECC composite material formed by the combination of smart materials such as shape memory alloy (SMA) and high ductility engineered cementitious composite (ECC) not only has good energy dissipation capacity, but also can obtain superior self-centering ability and damage self-healing ability, thereby improving the seismic performance and durability of shear wall structures. In this paper, in order to explore the nonlinear behavior of the self-centering shear wall under earthquake action and accurately simulate it, ECC and SMA material tests are carried out to establish the uniaxial constitutive relationship of the material. Using OpenSees finite element analysis platform, considering the micro and macro perspectives, a variety of finite element models are established, namely layered shell model, fiber model and multi-vertical rod model. Combined with the low-cycle reciprocating loading test of shear walls, the numerical simulation results are compared with the experimental data. By considering the parameters such as yield load, peak load and simulation time, the feasibility, stability and calculation efficiency of these models are evaluated. The results show that among the three models, the model based on fiber element can capture well the hysteretic response of new materials, and simulate the hysteretic performance, pinch effect and stiffness degradation of various shear wall members. The simulated values and experimental values can be well matched. Compared with the microscopic model, the computational efficiency of the fiber model is greatly improved, and the model has good feasibility, accuracy and efficiency.This work provides a basis for further research on the optimization of design parameters of SMA-ECC shear wall.

Experimental investigation and analytical model for the shear behavior of composite beams with prefabricated U‐shaped RPC permanent formworks

AbstractThis study aimed to investigate the shear performance of composite beams with prefabricated U‐shaped reactive powder concrete (RPC) permanent formworks with normal strength concrete poured inside. Three‐point bending tests were performed on eight composite beams with prefabricated U‐shaped RPC‐reinforced formworks and one reinforce concrete beam. Additional parameters, such as the stirrup spacing, shear span ratio, and inner core concrete strength, were evaluated. The test results indicated that the prefabricated U‐shaped RPC permanent formworks increased the shear capacity of the composite beams. Under the same configuration, the bending cracking load, stirrup yield load, and peak load of the composite beams increased by 51.54%, 88.02%, and 78.38%, respectively. An analytical model was proposed to predict the shear strength of composite beams with prefabricated U‐shaped RPC formwork and validated using the experimental results.

Eccentric load bearing performance of high bolt screw (HBS) active joints for prestressed internal supports in the subway excavation

This study introduces a novel High Bolt-Screw (HBS) active joint for enhancing the load-bearing performance of steel support systems used in subway foundation pits. The HBS joint addresses the limitations of traditional steel wedge joints, particularly in handling eccentric loads and tensile forces. Experimental and numerical analyses were conducted on specimens with different screw diameters to evaluate the mechanical behavior of the HBS joint under eccentric compression. Load-strain curves, load-displacement curves, and failure modes were documented to compare the performance of the HBS joint with an equal length steel support (ELSS) and a traditional wedge joint. The data and results obtained from numerical simulations exhibited a high degree of concordance with those derived from laboratory tests. Finite Element Analysis (FEA) was employed to perform parametric studies, examining the effects of key design factors such as screw diameter and eccentricity. The results indicate that the HBS joint provides superior preloaded axial force retention. Additionally, the HBS joint exhibited a yield load 1.35 times greater than that of traditional wedge joints, with an initial compressive stiffness 3.5 times higher, enhancing its resistance to deformation under eccentric loads. Parametric analysis indicated that the yield load is influenced by the eccentric distance but unaffected by the eccentric angle, with screw diameter, barrel nut height, and extension length identified as key factors. A yield load formula was derived through rigorous theoretical analysis and validated against experimental data, showing a relative error of less than 10 %. These findings emphasize the exceptional eccentric load-bearing capacity and stiffness of HBS joints, providing valuable insights for designing and implementing advanced support systems in subway foundation pit construction.

Mathematical model and experimental verification of self-centering energy dissipative brace equipped with disc spring and wedge block

The novel self-centering energy dissipation brace composed of disc spring group and wedge block group (DW-SCB) is introduced. The working mechanism of the DW-SCB and the force mechanism of each component are described. The stress analysis of the disc spring group (DSG) and the wedge block group (WBG) were carried out, and the DW-SCB theoretical prediction model was established. Three specimens with different disc spring preload lengths were fabricated, tested, and discussed. Furthermore, the established theoretical model was verified, and the theoretical model correction method considering the processing and assembly errors of the DSG was proposed. The tested data show that the hysteresis curve of DW-SCB is a typical flag shape, and there is almost no residual displacement after multiple loading. An increase in the preload length of the disc spring increases the yield load and bearing capacity of the DW-SCB but has no change on the stiffness of DW-SCB. All the components of the three specimens were not damaged after multiple loadings, which show that the DW-SCB has stable multiple seismic performance and recoverability. Significant, although the machining error of the disc spring leads to a large error between the experimental and theoretical curve of the DSG, the error correction method of the DSG proposed in this study can improve the prediction accuracy of the theoretical model, making the DW-SCB theoretical prediction model more accurate and reliable. The theoretical model considering the error of DSG can better predict the stiffness and load of DW-SCB, which can provide a reference for engineering design and application.

Study on Flexural Capacity of UHPC-NC Composite Slab with Reinforced Truss in the Normal Section

Ultra-high-performance concrete (UHPC) exhibits significantly higher tensile strength compared to normal concrete (NC). In this paper, the application of UHPC to the precast base plate of composite slabs was proposed, leading to the development of a reinforced truss UHPC-NC composite slab. This approach effectively enhanced the crack resistance of the slab. A finite element model (FEM) for the reinforced truss UHPC-NC composite slab was developed based on the ABAQUS (2016) platform, using appropriate material constitutive relationships for UHPC, NC, and steel reinforcement. The validity of the model was verified through comparison with relevant test results. Subsequently, the effects of parameters such as the cross-sectional area of the upper and lower truss chords, the reinforcement ratio of the precast base plate, the strength grade of the UHPC base plate, and the thickness of the UHPC base plate on the flexural capacity of the UHPC-NC composite slab were investigated. Finally, the equations for calculating the flexural capacity of the UHPC-NC composite slab were proposed. It was found that increasing the cross-sectional area of the lower truss chord improved the flexural capacity and stiffness of such slabs to some extent, though ductility was slightly reduced. On the other hand, increasing the upper chord cross-sectional area had limited impact on the flexural performance. Increasing the reinforcement ratio of the longitudinal reinforcement in the precast base plate significantly enhanced the load-bearing capacity and stiffness but similarly reduced ductility. As the UHPC grade of the precast base plate increased, the cracking load, yield load, and ultimate load of the slab also increased. However, when the UHPC grade exceeded C120, the improvement in flexural capacity became less significant. With an increase in thickness of the precast UHPC base plate, cracking, yield, and ultimate loads also rose, but ductility decreased. When the thickness of UHPC exceeded 60 mm, the increase in flexural capacity became modest. The proposed equations for calculating the flexural capacity of the reinforced truss UHPC-NC composite slab in the normal section agreed well with simulation results, providing theoretical and numerical support for the design and analysis of UHPC-NC composite slabs.

Flexural performance of a novel bolted inter-module connection affected by corner fitting openings

Modular Steel Buildings (MSBs) are innovative structures composed of prefabricated components. The inter-module connections (IMCs) are crucial for convenient on-site assembly and overall structural integrity. Numerous IMCs exhibit openings in corner fittings to provide construction space, which reduces the strength and stiffness. The effect of these openings on flexural performance, however, remains unquantified. This study, therefore, examines the impact of opening size on the flexural performance of corner fittings, using a novel bolted IMC as an example. Flexural performance was assessed using horizontal monotonic loading tests on three specimens, with variables including box length and opening size. The failure modes, load-displacement curves, rotational stiffness, and strain responses were obtained. Subsequently, a detailed finite element (FE) model, validated against experimental data, enabled a parametric analysis on bolt sizes, end plate thickness, and opening width. Parametric analysis indicates that increasing the end plate thickness from 14 mm to 20 mm raises ultimate load-bearing capacity by 85.51 % and stiffness by 82.95 %. Theoretical formulas based on yield line theory and the component method were derived to evaluate yield load-bearing capacity and initial rotational stiffness of IMCs, considering the effect of opening size. Comparsion of these formulas with experimental and FE model resuts demonstrated good accuracy, with deviations of 9.96 % for initial rotational stiffness and 12.13 % for yield load capacity, respectively. Finally, the working mechanism by which openings influence the flexural performance of IMCs is further discussed and clarified.

Enhancing the local compressive strength perpendicular to the grain of inorganic-bonded bamboo composite using glued-in rods

The inorganic-bonded bamboo composite (InorgBam) is a novel environmentally friendly engineered bamboo product manufactured from the bamboo fiber bundles glued together with magnesium oxysulfide (MOS) inorganic adhesive. Similar to raw bamboo culms, InorgBam exhibits significant material anisotropy that the compressive strength perpendicular-to-grain typically lower than that parallel-to-grain. To enhance the local compressive performance perpendicular-to-grain of InorgBam, the glued-in rods (GiRs) method was adopted, and the local compression test was conducted with various loading forms and GiRs parameters in this paper. Experimental results indicate that the GiRs method significantly enhances the local compressive strength and the deformation resistance perpendicular to the grain of InorgBam material. The replacement ratio and depth of GiRs are the major impact factors for enhancing the load-carrying capacity. The compressive ultimate load, yield load, and initial stiffness of the GiRs enhanced specimens increased by 167 %, 190 %, and 103 %, respectively. Furthermore, a universal predicted method of the yield load for local compression perpendicular to the grain of InorgBam material enhanced by GiRs was proposed considering the replacement ratio and depth of GiRs. The results herein can provide a basis expansion of the methods in enhancing the compressive properties perpendicular-to-grain of engineered bamboo materials.

Loading mechanism of timber screw–adhesive composite joint

The impact of carbon emission and other pollution generated by the construction industry on the natural environment and ecosystems is immeasurable. Wood, as a renewable building material with excellent performance, is a practical solution for future low-carbon buildings. Current screwed wood connections have good ductility, but the initial stiffness is relatively low. In this paper, composite wood connections with screw and adhesive were proposed and investigated. Static loading tests were conducted to screwed connections and composite connection specimens. The failure modes of different connection types, as well as the effects of adhesive type and adhesive connection area on the joint bearing capacity are discussed. The results show that the yield load and ultimate load of the composite joint made with the existing adhesive increased by up to 169% and 222%, respectively, compared with the screw connection. At the same time, the influence of curing time and bonding should also be taken into consideration. This study provides a foundation for wood joint design and promotes the sustainable development of the building industry.

Pilot study on the in-vitro effect of radiation therapy on bending stiffness of intramedullary photodynamic implants

Photodynamic implants are an increasingly popular minimally invasive option for the surgical treatment of metastatic bone disease. Following surgery, adjuvant radiation therapy (RT) is frequently administered to achieve better disease control and improve patient quality of life, but the role of RT in implant failures associated with photodynamic implants remains unclear. The aim of this study is to determine if the therapeutic RT range of 10–50 Gy affects the biomechanical properties of photodynamic implants. For the experimental group, 15 photodynamic implants were divided evenly into 5 groups that were exposed to different doses of RT (10, 20, 30, 40 and 50 Gy). The control group consisted of 14 non-irradiated photodynamic implants. Four-point bending tests were conducted on all implants to determine bending stiffness. One-way ANOVA was conducted. Bending stiffness (N/mm) mean ± standard deviation for the non-irradiated control group was 38.0 ± 1.2. Bending stiffness (N/mm) mean ± standard deviation for the irradiated experimental groups was 39.2 ± 1.0. No significant difference was found between any groups. RT doses at a range of 10–50 Gy do not affect the bending stiffness of photodynamic implants. The yield and ultimate failure loads were 263.4 ± 5.2 (N) and 305.9 ± 5.5 (N) in the non-irradiated group vs. 266.8 ± 6.4 (N) and 306.8 ± 6.4 (N) in the irradiated group, respectively. The lack of statistical significance in the difference in stiffness, yield, and ultimate load properties among the groups means that it is less likely that RT at the evaluated doses contributes to intrinsic implant failure. Further studies need to be conducted to conclude the potential effect of RT on other mechanical properties of photodynamic implants.

Comparative efficacy of Knema retusa extract delivery via PEG-b-PCL, niosome, and their combination against Acanthamoeba triangularis genotype T4: characterization, inhibition, anti-adhesion, and cytotoxic activity.

Acanthamoeba spp. is a waterborne, opportunistic protozoan that can cause amebic keratitis and granulomatous amebic encephalitis. Knema retusa is a native tree in Malaysia, and its extracts possess a broad range of biological activities. Niosomes are non-ionic surfactant-based vesicle formations and suggest a future targeted drug delivery system. Copolymer micelle (poly(ethylene glycol)-block-poly(ɛ-caprolactone); PEG-b-PCL) is also a key constituent of niosome and supports high stability and drug efficacy. To establish Knema retusa extract (KRe) loading in diverse nanocarriers via niosome, PEG-b-PCL micelle, and their combination and to study the effect of all types of nanoparticles (NPs) on Acanthamoeba viability, adherent ability, elimination of adherence, and cytotoxicity. In this study, we characterized niosomes, PEG-b-PCL, and their combination loaded with KRe and tested the effect of these NPs on Acanthamoeba triangularis stages. KRe-loaded PEG-b-PCL, KRe-loaded niosome, and KRe-loaded PEG-b-PCL plus niosome were synthesized and characterized regarding particle size and charge, yield, encapsulation efficiency (EE), and drug loading content (DLC). The effect of these KRe-loaded NPs on trophozoite and cystic forms of A.triangularis was assessed through assays of minimal inhibitory concentration (MIC), using trypan blue exclusion to determine the viability. The effect of KRe-loaded NPs was also determined on A.triangularis trophozoite for 24-72 h. Additionally, the anti-adhesion activity of the KRe-loaded niosome on trophozoites was also performed on a 96-well plate. Cytotoxicity activity of KRe-loaded NPs was assessed on VERO and HaCaT cells using MTT assay. KRe-loaded niosome demonstrated a higher yielded (87.93 ±6.03%) at 286nm UV-Vis detection and exhibited a larger size (199.3 ±29.98 nm) and DLC (19.63±1.84%) compared to KRe-loaded PEG-b-PCL (45.2 ±10.07 nm and 2.15±0.25%). The EE (%) of KRe-loaded niosome was 63.67 ±4.04, which was significantly lower than that of the combination of PEG-b-PCL and niosome (79.67±2.08). However, the particle charge of these NPs was similar (-28.2 ±3.68 mV and -28.5 ±4.88, respectively). Additionally, KRe-loaded niosome and KRe-loaded PEG-b-PCL plus niosome exhibited a lower MIC at 24 h (0.25 mg/mL), inhibiting 90-100% of Acanthamoeba trophozoites which lasted 72 h. KRe-loaded niosome affected adherence by around 40-60% at 0.125-0.25 mg/mL and removed Acanthamoeba adhesion on the surface by about 90% at 0.5 mg/mL. Cell viability of VERO and HaCaT cells treated with 0.125 mg/mL of KRe-loaded niosome and KRe-loaded PEG-b-PCL plus niosome exceeded 80%. Indeed, niosome and niosome plus PEG-b-PCL were suitable nanocarrier-loaded KRe, and they had a greater nanoparticle property to test with high activities against A. triangularis on the reduction of adherence ability and demonstration of its low toxicity to VERO and HaCaT cells.

Ex Vivo Biomechanical Comparison of Four Techniques to Tibiotarsus Osteosynthesis in Adult Laying Hens (Gallus gallus domesticus).

To assess the biomechanical parameters of intact tibiotarsi (INT) and tibiotarsi with a 5-mm segmental diaphyseal defect repaired using four osteosynthesis techniques: a locking plate (LP), a plate-rod combination, an external skeletal fixator (one end-threaded positive-profile pin per fragment) with an intramedullary pin tie-in (TIF 1), and an external skeletal fixator (two end-threaded positive-profile pins per fragment) with an intramedullary pin tie-in (TIF 2). Sixty tibiotarsi from 30 adult laying hens were allocated into five groups for nondestructive dynamic torsion and four-point bending tests, followed by failure tests. Nondestructive dynamic tests evaluated stiffness over time in torsion and bending. Torsion destructive tests provided maximum torque and rotation values, whereas the four-point bending tests provided the yield load, maximum bending load, and maximum displacement. The INT group showed higher torsional stiffness and maximum torque but similar bending stiffness, torsional strength, and bending strength in one or more groups. LP and TIF 2 exhibited the highest similarity frequencies among the treatment groups, whereas the TIF 1 group displayed lower stiffness and strength for most of the evaluated parameters. Similar results for LP and TIF-2 groups suggest the biomechanical equivalence of these methods for tibiotarsal osteosynthesis in adult hens.

Behavior of laminated bamboo columns under low cyclic reversed loading

Laminated bamboo, a type of eco-friendly engineered bamboo product, is increasingly gaining attention in the field of civil engineering. Although there has been considerable research on the material properties of laminated bamboo, studies focusing on the seismic performance of laminated bamboo columns are still relatively scarce. This paper discusses in detail the behavior of laminated bamboo columns and BFRP (Basalt fiber reinforced polymer) reinforced laminated bamboo columns under low cyclic reversed loading. In particular, the effects of slenderness ratio and axial compression ratio on laminated bamboo columns and BFRP reinforced laminated bamboo columns are studied. The hysteresis behavior of the column specimens is first tested through experiments. The results show that under low cyclic reverse loading, the failure of laminated bamboo columns is due to the tensile fracture and compressive bending of bamboo strips, as well as the tensile fracture of BFRP. To quantify the mechanical performance of laminated bamboo columns, parameters of interest are defined and discussed, including load-bearing capacity, stiffness, energy dissipation, and equivalent viscous damping. The load-bearing capacity and stiffness of laminated bamboo columns and BFRP reinforced laminated bamboo columns are significantly affected by the slenderness ratio and axial compression ratio. The yield loads for the column specimens with slenderness ratios of 37.0, 63.4, and 77.5 are within the ranges of 2.08–7.64 kN, 1.63–5.15 kN, and 1.82–7.51 kN, respectively. Laminated bamboo columns exhibit a satisfactory energy dissipation, with the maximum observed equivalent viscous damping exceeding 50 %. Furthermore, combining theoretical calculations and fitting analysis, bilinear skeleton curve models for both laminated bamboo columns and BFRP reinforced laminated bamboo columns are presented, showing a good agreement with experimental results. This research aims to provide some references for the design of laminated bamboo structures in future practical engineering.

Plastic mechanism models for use in DSM localised loading design of hat sections

The Direct Strength Method (DSM) of design has been recently developed for the design of cold-formed steel members under localised loading. The method requires a yield load (Py) and an elastic buckling load (Pcr) as input variables to the DSM design equations. This paper summarises test results used to develop plastic mechanism models for calculating Py for hat sections subject to practical loading cases. All four loading cases, including Interior Two Flange (ITF), End Two Flange (ETF), Interior One Flange (IOF) and End One Flange (EOF) loading cases were investigated. The yield/plastic mechanism behaviour of multiple web sections is not yet fully understood, while several publications in the literature have discussed the mechanical behaviour of hat sections under localised loading. Hence, this paper explains and proposes a plastic mechanism model based on the experimental data for calculating the yield load (Py) to be used in the DSM for localised loading design of hat sections in conjunction with the elastic buckling load Pcr.

Experimental Investigations of Seismic Performance of Girder–Integral Abutment–Reinforced-Concrete Pile–Soil Systems

Integral abutment bridges (IABs) have been widely applied in bridge engineering because of their excellent seismic performance, long service life, and low maintenance cost. The superstructure and substructure of an IAB are integrally connected to reduce the possibility of collapse or girders falling during an earthquake. The soil behind the abutment can provide a damping effect to reduce the deformation of the structure under a seismic load. Girders have not been considered in some of the existing published experimental tests on integral abutment–reinforced-concrete (RC) pile (IAP)–soil systems, which may not accurately represent real conditions. A pseudo-static low-cycle test on a girder–integral abutment–RC pile (GIAP)–soil system was conducted for an IAB in China. The experiment’s results for the GIAP specimen were compared with those of the IAP specimen, including the failure mode, hysteretic curve, energy dissipation capacity, skeleton curve, stiffness degradation, and displacement ductility. The test results indicate that the failure modes of both specimens were different. For the IAP specimen, the pile cracked at a displacement of +2 mm, while the abutment did not crack during the test. For the GIAP specimen, the pile cracked at a displacement of −8 mm, and the abutment cracked at a displacement of 50 mm. The failure mode of the specimen changed from severe damage to the pile top under a small displacement to damage to both the abutment and pile top under a large displacement. Compared with the IAP specimen, the initial stiffness under positive horizontal displacement (39.2%), residual force accumulation (22.6%), residual deformation (12.6%), range of the elastoplastic stage in the skeleton curve, and stiffness degradation of the GIAP specimen were smaller; however, the initial stiffness under negative horizontal displacement (112.6%), displacement ductility coefficient (67.2%), average equivalent viscous damping ratio (30.8%), yield load (20.4%), ultimate load (7.8%), and range of the elastic stage in the skeleton curve of the GIAP specimen were larger. In summary, the seismic performance of the GIAP–soil system was better than that of the IAP–soil system. Therefore, to accurately reflect the seismic performance of GIAP–soil systems in IABs, it is suggested to consider the influence of the girder.

Impact of Bond-Slip Models on Debonding Behavior in Strengthened RC Slabs Using Recycled Waste Fishing Net Sheets.

This study investigated the performance of recycled waste fishing net sheets (WSs) as a sustainable strengthening material for reinforced concrete (RC) slabs. The primary challenge addressed is the debonding failure caused by the low bond strength at the WS-to-concrete interface. To analyze this, two full-scale RC slabs-one with and one without strengthening-were cast and tested under a four-point bending setup. Finite element (FE) models incorporating existing bond-slip laws were developed using the ABAQUS software to simulate the strengthened slab's behavior. A sensitivity analysis was performed to assess the impact of bond-slip parameters on the failure mechanism. Experimental results indicated that the WS-strengthened slab enhanced the RC slab capacities by 15% in yield load and 13% in initial stiffness. Furthermore, the maximum shear stress of 0.5τmax or interfacial fracture energy of 0.2Gf, compared to values proposed by Monti et al., enabled the simulation of the global response observed in the experiment.

Study on seismic performance of a novel connection for exterior wall panels

In order to avoid the damage of the external wall panel and connecting joints caused by the incompatibility between the steel structure and the external wall panel under earthquake loads, as well as to control the interaction between the structure and wall panel to ensure favorable impacts on the main structure, a new connection for external wall panel is proposed. This connection combines the features of the sliding connection and the energy dissipating connection. To investigate the deformation behavior, failure modes, and energy dissipation capacity of the connection, a total of ten specimens with different parameters were designed for cyclic loading. The results indicate that the new connection dissipates energy through bending plastic deformation and pull-bending plastic deformation of the side plate, demonstrating excellent deformation and energy dissipation capacity with noticeable post-yield strengthening effect. Additionally, the effects of different geometric parameters on the initial stiffness, yield load, bearing capacity and hysteretic properties of the connections are also analyzed. Finally, based on the theoretical model of the space rigid frame, the calculation formula of the characteristic parameters at elastic stage of the joint is proposed by the assumptions of ignoring torsion, axial and shear deformation, which is validated by the test results and finite element simulation.

Research on Coordinated Relationship Between Deformation and Force in Shaft Foundation Pit Support Structures

In order to investigate the coordinated relationship between lateral deformation of the diaphragm wall and axial force of the internal strut, this paper first carried out a scaled model test on the mechanical features of a foundation pit support system based on a novel axial force servo device. Then, a finite element model was established to simulate the scaled model test, and the correctness of the finite element modeling approach was validated by comparing test results. After that, the same finite element modeling method was used to analyze the coordinated relationship between axial force and lateral deformation in the prototype foundation pit support structure. The results show that the axial force of the inner strut is negatively correlated with the lateral deformation in the diaphragm wall. The initial maximum lateral deformation in the diaphragm wall of the shaft foundation pit occurs at the bottom of the foundation pit, so changing the length of bottom strut simultaneously is the most effective way to adjust the mechanical behavior of the support structure. Under various support conditions, the maximum lateral deformation of the diaphragm wall in the prototype project is 0.59~0.66‰ of the total excavation depth of the foundation pit, and the maximum axial force of internal support is 11~30% of the yield load of a single steel strut.

Experimental Study on the Mechanical Properties of Squat RC Shear Walls with Corrosion Along the Base

In corrosive environments containing chloride and sulfate, the corrosion of steel bars is common along the base of squat RC shear walls (SRCSW) due to problems such as construction quality, concrete stress concentration, local defects, and accumulation of water and corrosive media. In this paper, three SRCSWs are designed and constructed and their mechanical properties assessed. One side of each SRCSW was exposed to a corrosive environment for 70 days, while the other side was subject to the same conditions over different corrosion times (i.e., 0 day, 42 days, and 70 days). Then, the corrosion-induced cracking process, the mechanical properties of SRCSWs corroded along the base, the relationship between the mass loss of total steel bars (MLTSB) in the corroded area and the wall mechanical properties, and the relationship between the average width of corrosion-induced cracks (CICs) and the wall mechanical properties were studied through an accelerated corrosion test and a loading failure test. The results indicate that the area of corrosion-induced cracking on SRCSWs increased with the corrosion time, and the cracking area on the different SRCSWs was approximately identical when the SRCSWs were exposed to the same corrosion time. When the degree of corrosion was different, the loading failure characteristics of the SRCSWs were obviously different, but the failure mode always corresponded to shear failure. The load–displacement curves of the SRCSWs with different degrees of corrosion along the base basically coincided and were linear when the loading was in the elastic stage. Compared to SW-1, the peak load of SW-2 decreased by 4.0%, but that of SW-3 increased by 2.7%. Compared to SW-1, the yield loads of SW-2 and SW-3 decreased by 22.4% and 11.8%, respectively. When the MLTSB increased from 13.05% to 16.71%, the crack, yield, and peak loads of the SRCSWs corroded along the base decreased by 8.8%, 22.4%, and 6.8%, respectively. The cracking, yield, and peak loads of the SRCSWs corroded along the base decreased linearly with the increase in MLTSB and the average width of the CICs, and the corresponding fitting relations were established. The results of this study can serve as a reference for the durability design of SRCSWs in corrosive environments.

Parameters Affecting Seismic Performance of Longitudinally Connected Track Lateral Blocks on Bridges Under Low-Cycle Reciprocating Loads

In the current seismic analysis of high-speed railway track–bridge structures, the constitutive parameters of track lateral blocks (TLBs) are not uniform. A finite element model of the TLB’s main beam is established, which considers concrete plastic damage, interface bond between old and new concrete, and bond slip between anchorage steel bars (ASBs) and concrete. Quasi-static tests of nine TLBs with different numbers and ASB diameters at a 1:2 scale was carried out to verify the accuracy of the TLB finite element model in terms of the failure pattern, interface damage, hysteretic properties, and skeleton model. Based on the verified TLB finite element model, the influence of different TLB design parameters on its seismic performance parameters was studied. The results show that the established TLB finite element model is in good agreement with the test data in terms of failure pattern, interface damage, hysteretic properties, and skeleton model, which verifies the accuracy of the TLB finite element model. ASB number has the greatest influence on the TLB yield load, followed by ASB diameter, concrete strength, ASB strength, and ASB spacing. ASB diameter has the greatest influence on the TLB peak load, followed by ASB number, ASB strength, concrete strength, and ASB spacing. ASB diameter has the greatest influence on the TLB energy dissipation capacity, followed by ASB number, concrete strength, ASB strength, and ASB spacing. With the increase in concrete strength and ASB strength, TLB ductility decreases. When the ASB number is higher than eight or the diameter is higher than 12 mm and the corresponding interfacial steel bar ratio reaches 0.82%, the TLB ductility will decrease.