Abstract:UHPC is a cement-based material with ultra-high mechanical performance and ultra-long durability, and it provides new possibility for innovation and performance promotion in bridge structures. In recent years，both domestic and oversea scholars have continuously performed a series of researches on UHPC in the field of bridge structures，driven relevant engineering applications，and made remarkable progresses. This paper introduces several new types of UHPC-based high performance bridge structures investigated by the authors’ research team，including the innovative UHPC strengthening structure for in-service steel bridge deck with fatigue cracking，UHPC strengthening structure for dangerous and degraded concrete bridges, UHPC bridge deck with shallow ribs，long-span UHPC box girder bridges，middle and short-span UHPC prefabricated bridges，UHPC-NC composite bridges，prefabricated UHPC cab beams，and UHPC anti-collision structures. The characteristic and advantage，theoretical and experimental researches，and engineering application of these new structures are systematically presented，aiming to provide experience for research and application of UHPC-based high performance bridge structures.

Abstract:In order to study the flexural performance of ultra-high performance concrete (UHPC) lowly ribbed deck panel and verify its feasibility in multi and long-span continuous beams, two different schemes of UHPC lowly ribbed deck panel were proposed based on the Bin Zhou Yellow River Bridge (average thickness: 16.4 cm and 14.3 cm). Firstly, the practical finite element model was established to obtain the stress of UHPC and the shearing force of headed studs. Secondly, two large-scale bending tests were carried out to obtain the crack initiation and development characteristics, the load-displacement curve, and the strain distribution law. The test shows that the bottom steel plate can resist the development of the crack. The crack width increases linearly with the load. The cracking stress of the two schemes is 16.8 MPa and 15.6 MPa, respectively, with a safety factor of 2.2 and 1.5. When the steel plate yielded, the main crack appeared rapidly, and specimens failed because the tensile crack developed rapidly and the compressive crack appeared. Then, after considering the contribution of UHPC tensile strength, the ultimate bending capacity was calculated by combing the UHPC specifications. The calculation result shows that when the factual material properties are considered, the ultimate capacity can be predicted well through the section nonlinear method. The ratios between the predicted result and experimental result are 0.95 and 1.01 respectively. Finally, the critical design parameters were analyzed. The result indicates that the influence of UHPC tensile strength is small. Increasing the thickness of the steel plate can be an effective way to improve the ultimate bending capacity. The narrow and high rib has higher force efficiency.

Abstract:This paper develops a novel continuous composite box girder bridge by combining ultra-high performance concrete (UHPC) with corrugated steel webs (CSWs) to overcome the weaknesses of traditional long-span prestressed concrete (PC) continuous girder bridges, such as excessive dead load and deflection at the mid-span, and cracking in the webs. The static and seismic performances of the CSWs-UHPC continuous composite box girder bridge are investigated. And its dynamic performance is compared to that of CSWs-normal concrete (NC) and PC continuous composite box girder bridges. The results reveal that: when compared, respectively, with the CSWs-NC composite box girder bridges and PC box girder bridges, the dead load of the proposed composite structure is reduced by 45% and 54%, the CSWs-UHPC composite continuous box girder bridge is highly durable, economically competitive throughout its life cycle. The static properties of the developed CSWs-UHPC composite structure meet the requirements of the specification. The ratio of the reasonable girder depth at the support to the mid-span（Hs /L） is 1/16 ~ 1/22, and the ratio of the reasonable girder depth at the mid-span to that at the support（Hm /Hs） is 1/1.5 ~ (-0.2+0.029L/Hs）. The CSWs-UHPC composite box girder bridge has a lower natural vibration frequency of transverse bending than the PC box girder bridge and a slightly greater natural vibration frequency of vertical bending than both the CSWs-NC composite box girder bridge and the PC box girder bridge. The lighter superstructure significantly reduces the inertia load, which makes the CSWs-UHPC composite box girder have excellent seismic performance. This new type of composite bridge can effectively address the issues previously mentioned for conventional long-span continuous bridges, as well as drastically minimize the seismic response. It will thus be a bridge type with competitive advantages over the traditional long-span continuous girder bridges.

Abstract:Aiming at the problems of complex force and easy cracking at the joints of prefabricated assembled bridge decks, a new type of ultra-high performance concrete (UHPC) dovetail joints was proposed. Through the load model test under the action of negative bending moment, the influence of different joint materials and prestress levels on the ultimate bearing capacity, failure form and crack distribution of UHPC wet joint bridge panels were studied. Based on the numerical simulation model verified by the experiment, the influence of different joint positions, joint forms, longitudinal reinforcement ratio, material strength, and thickness of the specimens on the bending performance of wet joints were compared and analyzed. The results showed that when the prestress was increased from 0 MPa to 5 MPa, the cracking stress and ultimate bearing capacity of the specimen were increased by 40.0% and 5.5%, respectively; The cracking stress of the dovetail joints was increased by 7.5% and 16.0%, respectively, and the bearing capacity was increased by 5.4% and 16.0%, respectively, when compared with the right angle joints and flat joints. Integrity of dovetail joints was good, and changing the joint position had little impact on the bending performance of the wet joint; The cracking stress and ultimate bearing capacity of the specimen increased with the increase of material strength, and the growth rate decreased when the material strength exceeds 120 MPa; The initial cracking stiffness of UHPC joints was about 90% of the initial stiffness, and the residual stiffness was about 25%; After the appearance of the first crack, the structural stiffness decreased rapidly, and after the longitudinal reinforcement yielded, the structural stiffness degradation rate was significantly slowed down, and the final stiffness remained at the residual stiffness; The ratio of the corresponding displacement of the ultimate load to the displacement of the cracking load was proposed as the expression form of UHPC wet joint bridge panels cracking ductility coefficient, and the results of crack ductility coefficient was 10.0~20.0, indicating that the post-cracking deformation ability of UHPC wet joint bridge panels was better.

Abstract:In order to study the flexural behavior of epoxy-joint segmental ultra-high performance concrete (UHPC) beams with external tendons, four-point bending experiments were completed for three UHPC beams with external tendons, including one monolithic beam and two segmental beams, and the main results such as the failure modes, load-deflection relationship and joint opening of the specimens were obtained. The epoxy-joint segmental UHPC beams mainly failed due to the damage of the epoxy as the joint was opened, which is different from the epoxy-joint segmental NC beams where the failure usually occurs in the NC near the joint. Considering the sectional pre-compression stress and the flexural tensile strength of epoxy, the calculation formula of the joint opening moment was proposed, and the difference between the calculation result and the experimental result was less than 1%, which was in good agreement. In order to accurately calculate the flexural capacity of segmental UHPC beams with external tendons, the Rod-Spring Hinge model that simplified the segments as rods and assumed the joints as spring hinges was proposed. Based on this model, the analytical method was used to derive the calculation formulae of stress variation and the secondary effect of external tendons. The difference between the theoretical and experimental values of tendon stress was less than 2.3%, which was in good agreement. Considering the uncertainty of segmental beams’ joint opening, a concept of the flexural capacity domain was proposed, i.e. the envelope range of structural flexural capacity under different joint opening conditions. The difference between the lower limit of the flexural capacity domain and the experimental values was less than 6%, so the lower limit is suggested as the reference value of the structural flexural capacity in a safe way. The above method can enrich the theory of calculating joint opening moment and structural flexural capacity for the epoxy-joint segmental UHPC beams with external tendons.

Abstract:In order to deeply study the shear performance of the steel-ultra-high performance concrete (UHPC) interface studs and the PBL hybrid shear bond, a practical calculation method is proposed to guide the engineering design and application. Based on the engineering background, 12 model specimens in 6 groups are designed and taken under push-out tests. The test results show that: (1) The load-slip curves of the stud shear key, PBL shear key, and the hybrid shear key of stud and PBL in UHPC have similar curve characteristics and can be divided into elastic, plastic damage, and three destruction stages. (2) In the service stage, the studs and the PBL in the mixed shear connector bear the load together, and the load sharing ratio is proportional to the respective stiffness. According to the theoretical analysis of the shear performance of the studs and PBL in UHPC, the practical experience formulas of the load-slip curves of the studs and PBL in UHPC, the calculation formula of shear capacity, and the recommended value method of shear stiffness are respectively proposed. The force distribution of each part of the stud and PBL hybrid shear connection is analyzed. Based on the principle of stiffness distribution according to the load, a practical empirical formula for the load-slip curve of the UHPC interface stud and the PBL hybrid shear key is proposed. Finally, the practical formula of the UHPC interface stud and PBL hybrid shear key proposed in this paper is used to check the actual bridge pier column, and it is shown that the shear safety factor is 2.17 and the shear slip is 0.04 mm, which is in line with the actual engineering bearing limit state and serviceability limit state requirements. This paper presents the calculation method of stud and PBL hybrid shear connector, which lays the foundation for its engineering application. Key words：bridge engineering；stud-PBL shear connector；experiment design；static analysis；failure mode；load-slip curve

Abstract:In order to reveal the influence law of the stud spacing on the behavior of steel-UHPC lightweight composite deck structures, variable amplitude fatigue tests were accomplished for three LWCD beam specimens and the stud spacing was chosen as the core parameter in the tests (i.e., 100 mm, 150 mm, 300 mm). In the fatigue tests, the influence of the stud spacing on the fatigue performance of the LWCD was revealed and the combined tension-shear fatigue properties of the steel deck plate at stud root positions were obtained. In the residual capacity test after the fatigue tests, the influence of stud spacing on the cracking evolution mechanism in UHPC and on the residual capacity of the specimens was captured. The fatigue tests indicated that when the stud spacing was 300 mm, the unit-load induced slips at the steel-UHPC interface were much higher than those in the other two specimens, but the slips did not increase significantly during the fatigue testing process. When the stud spacing was 100 mm or 150 mm, the strain at the bottom flange of the U rib did not exhibit significant change, and the strains increased slightly when the stud spacing was 300 mm. On the basis of the calculation method prescribed in the code of “Specifications for Design and Construction of Highway Steel-concrete Composite Bridge” in China, the combined tension-shear fatigue state of the steel deck plate at stud root positions was analyzed, and the results implied that this method could provide conservative results. In addition, the residual capacity test after the fatigue testing showed that the smaller the stud spacing, the smaller the interfacial slip and the higher the residual flexural capacity. On the basis of the elastic-to-plastic theory and plastic theory, the residual capacities of the specimens were predicted. It was revealed that although the specimens experienced a series of fatigue loading, the actual residual capacities obtained in the tests were still higher than the predicted values, and the plastic theory exhibits a better agreement relative to the test results.

Abstract:To study the bonding behaviors of the interface between steel rebar and ultra-high performance concrete (UHPC) for the thin and light reinforced UHPC members, several pull-out tests of reinforced UHPC specimens with different design variables, such as the diameter and cover thickness of steel rebar, and bonding length, were tested in this paper, and their influences of design variables on the bonding properties of the interface between steel rebar and UHPC are investigated. Based on the test results, the effect of each design parameter on the failure types, bond stress-slip curves, bond anchoring strength, and corresponding slip of the reinforced UHPC specimens is analyzed. The obtained results show that the changes in the rebar diameter, bonding length, and cover thickness have a great influence on the bonding behaviors of the interface between the steel rebar and UHPC. The ultimate bond strength and corresponding slip increase with the decrease in bond length, while it first increases and then decreases with the increase of the rebar diameter. The ultimate bond strength decreases with a reducing rebar cover thickness, while the corresponding slip increases. When the diameter is 12 mm and 16 mm, the cover thickness and the bonding anchor length of steel rebar should not be less than 1.5 times and 4 times of rebar diameter, respectively, while the bonding anchor length of the steel bar with a diameter of 8 mm should not be less than 3.5 times of the diameter. The calculation formulas of ultimate bond strength and critical anchorage length for the interface of reinforced UHPC are derived from mathematical statistics method, and they agree well with the test results.

Abstract:In order to study the interface mechanical behavior of ultra-high performance concrete (UHPC) filled square steel tube, 18 UHPC-filled steel tube specimens were designed for static push-out test, and the width-to-thickness ratio, height-to-width ratio, and the compressive strength of UHPC were considered as main parameters. The failure process and patterns, load-slip curves and bond strength of specimens, and the longitudinal strain of steel tubes were analyzed. The results show that the specimens are intact after the test and there is no visible local buckling on steel tubes, while some damage is formed around the edge concrete at the loading end. The load-slip curves are essentially the same at the loaded and free ends, and the curves are divided into two categories: weakened with a clear peak point and strengthened without a clear peak point. The bond strength decreases with the increase of the width-to-thickness ratio and height-to-width ratio. When the width-to-thickness ratios are large, increasing the strength of UHPC can significantly improve the bond strength. The longitudinal strain at the loading end of the steel tube is slightly larger than the value at the free end, which exhibits a negative exponent distribution along the height. Based on the composition of bond strength, the expressions of interface friction stress and mechanical interaction stress are determined by ignoring chemical adhesive force. The calculation model of bond strength for UHPC-filled square steel tube specimens under two curing conditions are respectively proposed, and the theoretical results agree well with the experimental data.

Abstract:In order to comprehensively solve the problems of concrete damage in the anchorage zone and the complicated welding process of embedded parts in the bridge expansion joint, two optimal schemes of ultra-high performance concrete (UHPC) expansion joint structures without welding on site were proposed: in optimal scheme 1, an anchorage reinforcement was arranged on one side of the anchorage plate and short studs on the other side; in optimal scheme 2, short studs were arranged on both sides of the anchorage plate, while long studs were added to the side of the section steel. In both schemes, the anchorage plates and embedded reinforcements were staggered, and the anchorage zone was poured with UHPC. The two optimal schemes make the construction operation simple and ensure the visualization of the installation quality. In order to explore the anchorage performance of the two optimal schemes and compare them with the traditional expansion joint, eight expansion joint specimens for a 1∶1 scale were tested. As for the traditional expansion joint, the anchorage reinforcement was welded on one side of the anchorage plate and the embedded reinforcement on the other side, and then the anchorage zone was poured with SFRC. The results show that the rigidity, strength, crack resistance, and anchorage performance of the two optimal schemes are significantly improved. The initial crack loads of the optimal scheme 1 and 2 are both 2.2 times that of the traditional one, while their ultimate bearing capacities are 1.38 times and 2.33 times that of the traditional, respectively. The cracks on the UHPC surface are relatively concentrated, small, and thin, but scattered, numerous and wide cracks on the SFRC surface. In optimal scheme 2, the long studs effectively limit the development of interface cracks. The comparative study shows that the two new schemes improve the mechanical performance and anchorage performance of expansion joints, without welding on site and high installation tolerance, which provide references for the design of bridge expansion joints

Abstract:RU-NC column is a new type of composite structure， which is composed of reinforced ultra-high performance concrete （RU） tube and normal concrete （NC） core column. In order to investigate the axial compression performance and the bearing capacity calculation method of RU-NC composite short columns， the axial compression test was carried out considering the experimental parameters， including wall thickness of UHPC tube， stirrup spacing and steel fiber volume fraction. While a comparative test of U-RC composite short columns composed of ultra-high performance concrete （U） tube and reinforced concrete （RC） core column reinforced with spiral stirrups was carried out. Therefore， numerical analysis was carried out based on the finite element modes established on ABAQUS software. The results show that the whole compression process of RU-NC composite short column could be divided into elastic stage， crack working stage and steel yield stage. Both RU tube and spiral stirrups have a certain constraint effect on the core concrete. The failure mode of composite column is characterized by that the RU tube and the concrete core were crushed， and the spiral stirrups were broken at the same time. Compared with U-RC composite short column， RU-NC composite short column with steel cages moving from core concrete to UHPC tube has better crack resistance， ductility and higher ultimate bearing capacity. The bearing capacity of RU-NC composite short column increases linearly with the increment of UHPC tube wall thickness and UHPC tensile strength， and shows a nonlinear trend with the decrease of stirrup spacing. The ultimate bearing capacity of RU-NC composite short column cannot be accurately calculated by using the current code and the existing literature algorithm. Based on the theoretical analysis of RU tube confined concrete， the axial compression bearing capacity algorithm of composite short column is proposed. The mean value of the ratio of the calculated value to the test results is 0.984， and the variance is 0.005 3， showing high accuracy， which can lay a foundation for the design and application of the new composite structure in the future.

Abstract:In order to study the simplified calculation methods of interlayer stresses for Super Toughness Concrete (STC) composite bridge deck pavement, finite element analysis was carried out by ANSYS software. The influence laws of steel -STC-SMA structure thickness, ambient temperature, and longitudinal slope on interlayer stress were discussed. The stress estimation models for STC composite bridge deck pavement were established. The simplified calculation formula of maximum shear stress and maximum normal tensile stress between layers were presented. The results show that the interlayer stresses are influenced by some factors such as the thickness of SMA and STC, environmental temperature, and longitudinal slope. Under the most unfavorable load combination, the maximum interlayer shear stress variation range is 0.38~0.55?MPa (normal temperature) or 0.35~0.55?MPa (high temperature), and the maximum normal tensile stress ranges from 0.18 to 0.23 MPa，when the deck longitudinal slope is not taken into account. The interlayer stress increases linearly with the increase of the longitudinal slope of the bridge deck. If the longitudinal slope increases from 0 % to 8%, the maximum layer shear stress is increased by 9.4% (normal temperature) or 12.0% (high temperature), and tensile stress by 12.0% (normal temperature) or 12.5% ??(high temperature). The general calculation formula of stress between deck pavement layers of the STC composite bridge is established by modifying the longitudinal slope degree. Compared with the finite element calculations of a real bridge, the error is less than 9%, indicating that the methods proposed in this paper can be used to estimate the interlayer stress of STC composite bridge deck under different longitudinal slopes.

Abstract:In order to explore the stress characteristics of the steel-concrete joint section， an experimental model of the steel-concrete joint section of the main beam with a scale ratio of 1∶3 （long × wide × height： 6.0 m × 1.722 m × 2.0 m）， and the four point bending negative moment bending test was carried out， and the stress condition and force transfer mechanism of the steel-concrete joint section under different load conditions were analyzed and compared， Based on the model test， ABAQUS is used to analyze the steel-concrete joint section. The research results show that under normal loading and over loading conditions， the stress level of each component in the steel-concrete joint section is low， the joint section has strong safety reserves， the bearing capacity of the joint section meets the design requirements， and the common stress performance between the steel box and the concrete is good. The bending moment borne by the steel top plate， bottom plate and UHPC layer of the steel-concrete joint section gradually decreases during the transmission from the steel beam transition section through the pressure bearing plate to the steel-concrete joint section， and the force transmission is smooth. The steel-concrete joint section of the test model is mainly loaded by the bearing plate， and the load sharing proportion is reasonable.

Abstract:The wind turbine is an atypical high-rise structure with a low damping ratio, and its seismic response spectrum is designed without considering the soil-structure interaction (SSI). Therefore, the seismic response spectrum of wind turbine design is proposed considering the SSI effect. 3 034 ground motions with different characteristics are selected and classified according to the building seismic code. Based on the S-R model, a single degree of freedom analysis model of wind power structure considering the SSI effect is established. Based on the statistical analysis of large sample local vibration results and the nonlinear least squares technique, the standard form of the new response spectrum is generated. The analysis shows that the proposed new response spectrum is larger than the standard one at a low damping ratio, and it is safe when compared with the traditional calculation based on the building seismic design code. The new response spectrum presented in this paper has a clear concept and simple form, which can provide a basis for the seismic design of wind power structures.

Abstract:Due to the aging of the in-service steel bridge deck, the size and density of widely distributed fatigue cracks at the weld gradually increase, leading to the interaction between the near-source multiple cracks. The coupling propagation and combination of multiple fatigue cracks are also promoted. In order to study the coupling propagation effect between multiple fatigue cracks, a numerical analysis model of two collinear fatigue cracks on steel bridge deck plate cover-U rib welding seam is established. Based on the theory of linear elastic fracture mechanics, ABAQUS-FRANC3D technology is used to calculate the stress intensity factor of single crack and two collinear cracks. The influence of crack spacing and size of interference crack on the propagation characteristics of the foundation crack is revealed, and the simulation conclusion is verified by a full-scale segmental test. The analysis results showed that the stress strengthening effect of collinear cracks cannot be ignored, compared with single crack. When all cracks have the same size, it is the most unfavorable case for multi-crack propagation. If the ratio of crack spacing to crack length s/c is less than 0.5, the stress intensity factor and crack growth rate are significantly affected by the coupling effect.

Abstract:This paper aims to investigate the general law of slope stability under pile foundation-induced loads and propose a calculation method of corresponding stability coefficients. Firstly, the finite element limit analysis method is introduced and verified by the case for the pile foundation in sloping ground. Next, some factors (e.g. lateral load atop the pile, cohesion, and the relative position between pile and slope) are normalized, and the calculation method of stability coefficients of the slope subjected to pile foundation-induced loads under various conditions is presented and expressed in tabular form. Then, the load impact factor is presented to characterize the effect of lateral loads atop piles on slope stability factors, while slope failure modes are explored, and the semi-experiential and semi-theoretical method of slope stability coefficient under loads induced by pile foundations are presented. Finally, the effect of lateral loads atop piles, the slope inclination, internal friction angle of soils, cohesion, and pile position on slope stability factors are discussed. The results show that the slope stability factors are positively correlated with internal friction angle and cohesion, and negatively correlated with lateral loads atop the pile. These above-mentioned analyses can provide references for bridge engineering design in the sloping ground, which are of certain theoretical and engineering application value.

Abstract:In this study, seven groups of three-dimensional finite differential numerical simulation tests were performed to investigate the dynamic characteristics of the composite foundations of geogrid-encased piles under cyclic loading. The effects of four important parameters on the behavior of the encased piles were evaluated. The numerical calculation results are compared with those of laboratory model tests, which verifies the rationality of the numerical results. The results show that the stress and settlement of encased stone piles composite foundations have obvious dynamic characteristics under cyclic loading. Under the same cyclic loading condition, increasing the gravel density could effectively improve the bearing capacity of the piles. The encasement can improve the mechanical properties of the piles, and the encasements with different lengths have different effects on the piles. Increasing the encasement length in a certain range can effectively improve the bearing capacity of the stone piles. The encasement has a significant effect on the cumulative settlement and stress concentration at the top of composite foundations. The encasement can improve the integrity of the stone piles, and increasing reinforcement length can lead to better vibration coordination of the stone piles. Pile diameter has an obvious influence on the cumulative settlement at the top of encased stone pile composite foundations, and the optimal L/d value of the stone pile is 8/3. The results of numerical calculation fit well with those of laboratory model tests. The maximum difference in settlement value is 7%, and the maximum difference in lateral stress of the pile is 9%.

Abstract:In order to solve the problem that the horizontal displacement of adjacent pile foundation gradually develops with time under the condition of foundation pit excavation in soft soil foundation, a two-stage method is used for analysis. In the first stage, a three-dimensional fractional Merchant viscoelastic model is introduced to describe the rheological properties of soft soil. Combining with the correspondence principle and the Laplace transformation method the Mindlin time-domain solution of the additional stress is obtained. In the second stage, regarding the pile foundation as Timoshenko beam on the Pasternak foundation, the additional stress is loaded on the pile foundation, and the differential equation of pile foundation deformation is established. On this basis, the time-domain solution of horizontal displacement of the pile foundation considering the shear effect of the pile foundation and the thickness of the pile-soil shear layer is obtained through the finite difference method. The correctness of the proposed method is verified by comparing it with the results of existing literature. Finally, the influencing factors of the three-dimensional fractional Merchant viscoelastic model parameters (shear modulus, volume modulus, viscosity coefficient, fractional order) are analyzed. The results show that the numerical solution can well reflect the development law of horizontal displacement of adjacent pile foundations caused by foundation pit excavation with time.

Abstract:According to the lateral bearing characteristics of bridge piles in sloping ground, the pile-soil interaction model considering the slope effect and the differential equation of flexural deformation was established. Based on the m method and transfer matrix method, the transfer matrix solution of pile internal force and displacement analysis was derived. The proportional coefficient of clay and sand slope foundation were measured by model tests. The relationship between the proportional coefficient of slope foundation and slope angles was obtained by nonlinear fitting, and then the rationality of theoretical solutions was verified by the model test. Based on an engineering example, the influence of slopes and horizontal loads on the internal force and deformation of piles in the sloping ground were analyzed. The results show that: the proportional coefficient of sloping ground decreases nonlinearly with the increase of horizontal displacement of the pile at the pile-soil interface. The proportion coefficients of clay and sand sloping grounds decrease with the increase of slope angles. The horizontal displacement of the pile top and the maximum bending moment of the pile body increase with the increase of slope angles and horizontal loads. When the slope angle increases from 0° to 60°, the horizontal displacement of the pile top increases by about 86.4%, the maximum bending moment of the pile body increases by about 4.6%, and the position of the maximum bending moment move down by about 2.0 m. When the horizontal load is increased by 50 kN, the horizontal displacement is increased by 48.5% and the maximum bending moment is increased by 41.6% on average.

Abstract:To investigate the effect law of surface roughness and soil relative density on the mechanical properties of sand-concrete pile interface, a series of sand-concrete interface tests with various surface roughness and soil relative densities were conducted by the large-scale direct shear apparatus. This study investigated the influence of roughness and soil relative density on shear stress-horizontal displacement, peak shear strength, secant friction angle, and normalized friction coefficient. The results showed that in the case of the smooth interface, the shear stress-horizontal displacement curves of the dense sand sample illustrated a slight softening response, and softening response became remarkable as the roughness increased. The curves of the loose sand sample showed a hardening response. Moreover，the peak shear strength of the interface increased nonlinearly with the increase of normal stress. And the greater the soil relative density，the more obvious the nonlinearity. The secant friction angle of the interface decayed exponentially with increasing normal stress. However, the peak friction coefficient decreased as a power function with the increasing normal stress due to the smaller shear strength increment. Additionally, there existed a critical value of roughness Icr，such that the peak friction coefficient and normalized secant friction angle no longer increased as the roughness increased and turned to decrease when I exceeded Icr.

Abstract:To study the effect of the replacement rate of sea sand on the properties of concrete in-depth, this paper uses three kinds of original sea sands from Jiaozhou-Shandong, Zhangzhou-Fujian, and Qinzhou-Guangxi to compare and study the differences of their physical properties after mixing with river sands. Meanwhile, these sea sands were used to replace river sand with 15%, 25%, 35%, and 50% replacement rates to study their effects on the workability and mechanical properties of concrete at different ages. The test results show that: the use of sea sand in concrete basically does not affect the workability of concrete, and the sea sand with a 50% replacement rate can improve the fluidity of concrete. With the increase of sea sand replacement rate, the compressive strength and splitting tensile strength of concrete increase and then decrease, but the replacement rate has less effect on the elastic modulus; the sea sand can optimize the distribution of fine aggregate particle size and improve the strengths of concrete. However, harmful components such as shells in sea sand can adversely affect the mechanical properties of concrete at a high replacement rate. In addition, the overall effect of the sea sand replacement rate on the strength of concrete (all within 10%) is limited, and sea sand with a 50% replacement rate is still higher than the control group at long curing age. Therefore, from the engineering application point of view, the sea sand replacement rate in a range of 50% is feasible.

Abstract:To solve the problem that the existing nondestructive testing (NDT) technology is difficult to accurately detect the early corrosion thickness of steel plate, based on the non-contact nondestructive terahertz time-domain spectroscopy (THz-TDS) technology, the optical parameters of corrosion products and the corrosion thickness of steel plate are detected by using the high transmission to non-polar materials and reflection to polar steel materials properties of terahertz (THz) waves. The experimental results show that when the effective frequency is within the range of 0.2-1.6 THz, the refractive index of the corrosion products is approximately 2.8. The relative amplitude of the first peak in the reflective THz signal has a logarithmic function relationship with the corrosion time of the steel plate and a linear relationship with the reciprocal of the corrosion time. The experimental results also show that the corrosion thickness increases linearly with the increase of corrosion time, and the accuracy of corrosion thickness measured by THz technology is more than 90%. The feasibility and accuracy of non-contact THz-TDS technology for corrosion thickness detection are therefore proved.

Abstract:：In order to improve the accuracy and effectiveness of structural model updating, a finite element model updating method based on modal parameters and a modified firefly algorithm is proposed, in which an objective function based on modal parameters is formulated and solved by the modified firefly algorithm. The modified firefly algorithm is compared to be accurate and superior to the original firefly algorithm, genetic algorithm, and particle swarm optimization in solving a numerical simulation example of a truss model. And it shows that the optimal solution obtained by the modified firefly algorithm is closer to the actual value, and the scatteredness is low, which proves the accuracy and effectiveness of the modified algorithm. Finally, the accuracy and effectiveness of this method in structural finite element model updating are verified by a damage identification test of a 6-DOF shear frame experimental model.

Abstract:To accurately evaluate the rationality of office buildings energy consumption with different use intensities, the building energy consumption software Designbuilder was used to analyze the impact of service time and personnel density on the subentry and total energy consumption of office buildings. Considering the influence of use density on subentry energy consumption, the energy consumption correction method for office buildings was optimized, which reduced the energy consumption correction value of the sample buildings with a large deviation of use intensity by 35%~45%. Using the reasonable operating energy consumption of the same type of buildings in the same climate zone as the baseline, an energy consumption evaluation method for office buildings was proposed. The new method helps to more accurately reflect the actual energy level of office buildings. The results can provide a reference for the refined evaluation of office building energy consumption.