FRP adhesive & bolted hybrid joint has the combined advantages of adhesive joints and bolted joints, which behave enhanced static performance, but its fatigue failure mechanism still needs to be studied. In order to study the fatigue performance of hybrid FRP joints under various working conditions, this study designed and manufactured single-lap hybrid FRP joints specimens. Firstly, the static load tests under axial tension loads and four side shear loads were carried out, and the corresponding failure modes and ultimate bearing capacity were obtained. Then, high cycle fatigue tests under two working conditions were carried out, and the damage process of the adhesive layer was measured by acoustic emission (AE) technology. The fatigue failure mode, characteristic fatigue life and stiffness degradation of the specimen were obtained, and the fatigue life prediction method was proposed. The results indicate that the anti- -fatigue performance of hybrid FRP joints is mainly controlled by bolted-connection, and its fatigue failure process can be divided into four stages: adhesive layer cumulative damage, adhesive layer failure, FRP cumulative damage, and FRP failure. Among them, the AE characteristic parameters of adhesive layer failure stage and FRP failure stage change significantly, and this can be used as the basis for identifying the failure occurrence. When the number of bolts is small, two working condition show the similar failure mode of the nut squeezing into the FRP plate. When the number of bolts is large, for tensile specimens, the tensile-shear failure mainly occurs at the hole of the FRP plate; for shear specimens, the failure mode is overall shear failure of FRP plate. The increase of the number of bolts can significantly improve the characteristic fatigue life of tensile specimens, and effectively inhibit the stiffness degradation during fatigue loads, but the improvement of fatigue performance of shear specimens is not obvious with the increasing number of bolts. The S-N curve of two working conditions obtained based on the test data can provide a reference for the fatigue life calculation of hybrid FRP joints, and help the application of such joints in bridges and other structures that mainly bear repeated loads.

Compressive strength is an important mechanical property of foamed lightweight soil. Accurately predicting and adjusting the compressive strength of lightweight foam soil is of great practical significance for improving construction efficiency. For intelligent control and optimization of foam light soil, this study designed a topology structure including 4 node input layer, 8 node hidden layer and 1 node output layer. The weight and threshold of BP neural network were improved by genetic algorithm (GA) in input layer. Using the four parameters of water-solid ratio, fly-ash ratio, fine aggregate mixing ratio and bubble rate as input parameters and 28-day compressive strength as output parameters, the two models before and after optimisation were validated and compared using mean squared error (MSE), coefficient of determination (R2) and relative error as samples. Based on this, a method for designing the mix ratio based on different performance requirements was established. The results show that compared with BP neural network, the GA-BP neural network has a larger fitness function value and smaller mean square deviation; the fit between the predicted and actual values can reach 0.946, with stronger prediction accuracy and gene-ralization ability; the global search ability of the genetic algorithm also makes up for the defect that BP neural network can easily fall into local optimum, and can better guide the fitting ratio design of the strength prediction of fly ash foam lightweight soil. The GA-BP neural network based strength growth prediction model for foam lightweight soils enables flexible adjustment of the compressive strength of foam lightweight soils, and it is of important refe-rence value for engineering construction.

In order to seek a reasonable and efficient prestress optimization method for cable domes, this paper proposed a new strategy for growth diffusion mechanism of large step and screening mechanism of growth points by analyzing the basic principle and algorithm mechanism of plant growth simulation algorithm (PGSA). On this basis, the plant growth simulation algorithm based on stage growth (stage growth PGSA) was established. This algorithm divides the optimization process into multiple stages and introduces the corresponding growth diffusion mechanism or screening mechanism of growth points in different stages. Firstly, the growth diffusion mechanism of large step was introduced to realize the spread of growth points by means of one-time diffusion growth with multiple steps. Then, the fast search was carried out with the medium step and the loose screening mechanism. Finally, the convergence was conducted with the small step for accuracy requirements and the strict screening mechanism. Thus, the prestress optimization of cable domes was done by using the stage growth PGSA and compared with other algorithms. The results show that the stage growth PGSA can effectively improve the global searching ability, reduce the growth space, and avoid growth points becoming saturated compared with the original PGSA. The number of calculation iteration of stage growth PGSA is the smallest and the initial strain energy of the structure after optimization is minimal in comparison with those of the multi-island genetic algorithm, adaptive simulated annealing algorithm, and particle swarm optimization algorithm. With its higher optimization efficiency and better optimization effect, therefore, this algorithm is applicable to the prestress optimization of cable domes.

Most of the existing studies on acid corrosion of concrete focus on the mechanical behavior of concrete structures without loading or under monotonic loading.In order to study the variation law of mechanical properties of in-service concrete members under cyclic loading，six groups of concrete prism specimens were prepared and immersed in hydrochloric acid of 1%（mass fraction）for accelerated corrosion.The monotonic and cyclic axial compression loading tests were carried out to examine the influence of corrosion on the mechanical properties of concrete under cyclic axial compression loading.Then，the concept of effective load-bearing cross-area ratio was proposed，and the descending correction coefficient of effective load-bearing cross-area ratio was introduced to establish the practical constitutive model of hydrochloric acid corrosion concrete under cyclic loading.And the model was verified.The results show that hydrochloric acid corrosion has a significant effect on the failure characteristics of concrete.The surface of corroded concrete is easy to peel off under loading effects，and the area of spalling enlarges gradually with the increase of loading.Meanwhile，with the increase of corrosion period，the compressive strength reduces of concrete obviously，and the bearing capacity decreases rapidly.The envelope of stress-strain curve of concrete with different corrosion ages under cyclic loading is basically consistent with that of the monotonic loading.However，the degradation rate of descending section for the stress-strain curve of concrete under cyclic loading is larger than that under monotonic loading due to the accumulation of internal damage of corroded concrete，and the failure is relatively more prominent.The peak strain of concrete under cyclic loading is slightly less than that of the monotonic loading.As the continuing increases of the corrosion period，the peak strain and ultimate strain of concrete under cyclic loading increase observably，while the peak stress and elastic modulus decrease significantly.Compared with uncorroded concrete，the test peak stress and elastic modulus of corroded concrete decreases by 53.25% and 74.1%，respectively，and meanwhile the peak strain and ultimate strain increased by 55.7% and 77.87%，respectively.The stress-strain curves calculated by using the model established in this paper match well with the test results，indicating the desirable fitting effect of the model.

In view of defects in the connection of concrete-filled steel tubular (CFST) composite column to concrete beam joint specified in the current code, this paper proposed a new type of fastener anchorage connection of beam to column joint with ring reinforcement in the column. The longitudinal reinforcement of the beam end of the concrete frame connected ring bar in column in forms of type, L-type and type and the ring bar set outside the steel pipe in the column was used to balance the tensile force from the beam end. Five specimens of concrete-filled steel tubular composite column concrete beam joints were designed for the monotonic static loading tests. The distribution and development of cracks, deformation, failure mode, bearing capacity, ductility of the middle joints and rebar strain development law were studied, and simulation analysis was performed using the ABAQUS software. The results show that ultimate failure modes of specimens with different joint anchorage are similar: the bending failure occurs at the end of beam, and all specimens possess good ductility and deformation ability. The yield of ring bars in columns lags behind the yield of longitudinal bars under tension, and no longitudinal bar slips off central bars during the test. The simulation results are consistent with the test results.

Under the actions of earthquakes, the damage distribution of Buckling-Restrained Braced Steel Frames (BRBFs) is usually not uniform. Once the beam-column joints or other components of BRBFs are destroyed, the high ductility of the buckling-restrained braces cannot be fully achieved. The local failure and the weak stories of BRBFs would cause the structures to collapse. Therefore, this paper proposed the scheme of two improved ductile beam-column joints and applied it in the BRBFs to achieve the high ductility by coordinating the global ductility of the structure and the local ductility of the ductile joints and members. Firstly, the finite element models of the BRBFs with ductility-enhanced joints were established, and the accuracy of the numerical model was verified. Secondly, the incremental dynamic analysis method was used to analyze the influence of the global ductility on the seismic collapse capacity resistance of the structural systems. Finally, the seismic collapse capacity of the structural system was evaluated based on the Collapse Margin Ratio (CMR). The results show that, compared to the BRBFs with rigid connections, the global ductility of BRBFs with the Reduced Beam Section (RBS) connections and the Top-Flange Beam Splice (TFBS) connections increase gradually. The CMR and the seismic collapse resistance capacity of BRBFs are improved with the increment of structural global ductility.

Prefabricated steel-concrete composite frames are increasingly applied in engineering day by day.However，research on their anti-collapse performance is less reported.To investigate their dynamic collapse perfor-mance，two reduced-scale prefabricated composite frame substructures were designed and tested by dynamically removing a column in this paper.Collapse behaviors of such frame structures under different load conditions were studied，and the effect of the division of precast concrete（PC）slabs on the dynamic collapse behaviors was also assessed.Then，a calculation model of the equivalent dynamic increase factor（DIF）of collapse load was built based on the experimental results for prefabricated composite frames.The results show that under the effects of one time collapse load（30 kN）and twice collapse load（60 kN），the primary structural damage for prefabricated steel-concrete frame substructures is the cracking of concrete slab at the beam ends close to the side column.After the middle column failed，the residual structures still have the superior load-bearing capacity and overall stiffness.The structures will not collapse under the two load conditions.The prefabricated composite frames are subjected to a greater impact effect under the same collapse load compared to the composite frames using cast-in-situ concrete.Division of the PC slabs slightly affect the dynamic characteristics of the composite frame substructures.However，it will lead to the increase of the strain dynamic increase factors of the steel girders and the longitudinal slab reinforcement.The increase factors of vertical displacement at the failed columns vary between 1.38 and 1.65 for the two substructures，and the dynamic increase factors of strain are even greater than 2.0 in some cases.The calculation model of the equivalent DIFs of collapse load for prefabricated composite frames developed based on the experimental results can provide a reference for the revision of the collapse load when the static collapse analysis is conducted.The calculated DIF of collapse load based on this model is conservative.

There is a close cross-scale relationship between fabric anisotropy of granular media and the macro-mechanical properties, and particle shape plays a significant role in the evolution of the fabric anisotropy. In addition to sphericity, angularity and roughness of particles, the authors found that the eccentricity in the particle morphology is also an important factor, and there were few studies on it so far. So in this paper, the open source aspheric DEM program SudoDEM was used to model eccentric particles based on poly-superellipsoids. A series of true triaxial simulations with different eccentricities were carried out, and the effects of eccentricity on the induced anisotropy of granular media were explored. The results show that the fabric anisotropy develops to varying degrees with the increase of eccentricity, leading to the development of macroscopic shear resistance of granular media. Meanwhile, the coordination number is larger, the proportion of sliding contacts is higher, and the grid inhomogeneity of the contact force is more obvious. This is mainly because the particle eccentricity enhances the interlocking between particles. Normal contact force has the largest weight in the induced anisotropy, while the normal branch vector remains basically isotropic. Anisotropy of tangential contact force and tangential branch vector are rather sensitive to the eccentricity, indicating that contribution of them to fabric anisotropy cannot be ignored. The increased weak contact and sliding contact proportions caused by the increased eccentricity also indirectly lead to transformation between the normal contact force anisotropy and tangential contact force anisotropy.

Compressive creep tests on thirty-seven recycled lump/aggregate concrete (RLAC) specimens were carried out to reveal the creep behavior of RLAC by taking the replacement ratio of demolished concrete lumps (DCLs), replacement ratio of recycled coarse aggregates (RCAs), replacement ratio of recycled sand rooted from alluvial-proluvial (A-P) soil, stress level and reinforcement ratio as parameters. The results show that the specific creep of reinforced/unreinforced RLAC is greater than that of reinforced/unreinforced recycled aggregate concrete (RAC). The increase rate of RLAC is 10.1% when unreinforced and the increase rate is 13.4% and 11.5% when the reinforcement ratio is 1.16% and 1.57%, respectively As the replacement ratio of RCAs in new concrete increased from 30% to 50%, the specific creep of reinforced/unreinforced RLAC increased by 7.4% and 11.4% respectively; when the fine aggregate (i.e., river sand) of new concrete is completely replaced by the recycled sand from A-P soil, the creep behavior of reinforced/unreinforced RLAC shows almost no change, but both of the shrinkage deformation decreased. As the reinforcement ratio increases from 1.16% to 1.57%, the specific creep of RLAC and RAC decrease by 5.0% and 6.6%, respectively. Reinforcement reduces the shrinkage deformation of RAC and RLAC, and the reduction grows with the increase of reinforcement ratio. As the replacement ratio of RCAs in new concrete increased from 30% to 50%, the elastic modulus of RLAC have little change and it is also almost free from the impact of replacing the fine aggregate (i.e., river sand) of new concrete with the recycled sand from A-P soil; and when the stress level is less than 0.4, the specific creep of RLAC is nearly deemed as irrelevant to the stress level.

Low frequency，broad bandwidth and adjustable frequency have always been adopted as crucial indexes to measure the performance of piezoelectric energy harvesters（PEHs）.The axial preload is deemed as one of the effective ways to improve these indexes.To explore the effect of preload on the energy harvesting characteristics，the electromechanical coupling governing equations were derived based on the Euler-Bernoulli beam theory and Gauss Theorem.The asymptotically analytic solutions of the displacement，the voltage and the average output po-wer were obtained with Galerkin discretization and the multi-scale approach.Then，through theoretical analysis，this paper obtained the expressions of the short-circuit and open-circuit resonance frequencies，the open-circuit voltage amplitude，the optimal output power and the optimal load resistance.For the cantilever beam model，the validity of the theory was verified by numerical simulation.Finally，the influence of preload on open-circuit voltage and optimal output power was analyzed.The results reveal that the axial preload can improve the energy harvesting efficiency of piezoelectric cantilever beam.Compared with the case without preload，the resonant frequency decreases by 31.6%，the amplitude of open-circuit voltage increases by 120.8%，and the optimal output power increases by 40.0%，when the preload is 20N.

In order to obtain the high-accuracy solution for control tension of each strand of stay-cables during construction, this paper studied the nonlinear relationships among the parameters describing the static state of cables and proposed a high-accuracy and non-iteration solving method for control tension of each steel strand. Based on the exact solution of the catenary of the cable shape, the high-precision and approximate solution of the stress-free length of the cable was solved by the Taylor expansion method. Based on the two basic principles of forward assembly analysis and equivalent tensioning method, the equivalent static state of steel strands during the construction process was obtained by recursive calculation when different steel strands were tensioned. The high-precision solution for the control tension of each steel strand was solved by approximating the unstressed cable length, the equivalent cross-sectional area and the projected length of the diagonal cable.Taking the stay-cables of the main bridge of the Honghe Bridge (a composite girder cable-stayed bridge with a main span of 500 meters) in Zhuhai city, the Jitimen Bridge (a prestressed concrete cable-stayed bridge with a main span of 210 meters) in Zhuhai city and cables mentioned in two literatures as examples, the error between the approximate solution of the method in this study and the exact solution of the catenary of iterative solution was calculated. The results show that the calculated error of the stress-free cable length between the method proposed in this paper and the catenary solution is less than 0.002%, and the tension error of each strand is less than 2%, which fully meet the accuracy requirements of construction. The method presented in this paper has the advantages of high precision and low calculation cost, so it has a high value of popularization and application.

This paper carried out a detailed study on the damping characteristics of the eddy current coupling beam damper, which can start to dissipate energy under small deformation of the replaceable coupling beam. Based on the analysis of magnetic circuit theory, the study proposed the optimal arrangement of permanent magnet pole in eddy current damper. In other words, the permanent magnet poles parallel to the direction of conductor motion were arranged alternately, and the permanent magnet poles perpendicular to the direction of conductor motion were arranged in the same direction. In view of this, two kinds of eddy current dampers were designed, one of which is the plate eddy current damper with the conductor plate moving straight in the magnetic field and the other is the rotary eddy current damper with the gear-rack mechanism to amplify the rotation speed of the conductor plate in the magnetic field. Two kinds of eddy current dampers were used in the replaceable coupling beam, and the finite element simulation of the new eddy current coupling beam damper installed on the replaceable coupling beam was carried out, which revealed the nonlinear mechanical behavior of eddy current damping. It shows that the damping coefficient and stiffness coefficient are strongly related to the frequency. The higher the loading frequency, the lower the energy consumption efficiency and the higher the dynamic stiffness of the structure. So, the eddy current damper is more suitable for low frequency working conditions, and at this time, the damping coefficient of the eddy current damper is large, the energy consumption efficiency is high, and the stiffness coefficient is small, which basically does not change the natural vibration characteristics of the structure. Therefore, it is of great value in real-world application.

The analysis of elasto-plastic solution can provide a basis for the stability research of cold regions tunnel. Therefore, the elasto-plastic damage mechanics calculation model was established by considering the non-uniform frost heave of surrounding rock. The unified analytical solutions of elasto-plastic stress field and displacement field of cold regions tunnel were derived based on the unified strength theory, and the unified solutions were verified and the parameters were analyzed. The results show that, by neglecting plastic damage and volume frost heave ratio of surrounding rock, the elasto-plastic solution of cold regions tunnel tends to be conservative, and the actual frost heave degree of surrounding rock for cold regions tunnel can be more accurately reflected by considering the non-uniform frost heave. In addition, the potential strength of frozen surrounding rock can be effectively improved by considering the intermediate principal stress effect. The radial stress σf of lining and plastic radius rp of tunnel are significantly influenced by parameters such as damage degree ratio λ/Ef, volume frost heaving ratio ξV, coefficient of non-uniform frost heaving k, unified strength theoretical parameter b, initial ground stress p0 and displacement release coefficient η. Hence, the influence of different parameters on tunnel engineering in cold regions should be reasonably analyzed. The research results can provide theoretical reference for engineering design of cold regions tunnel.

The main cable diameter of self-anchored suspension bridge is small and the vertical span ratio is large. In order to study the influence of the pre-tightening force loss caused by creep relaxation of the main cable clamp on the safety of the whole bridge，this study took the main cable clamp of Sanchaji Xiangjiang Bridge in Changsha as the research object, and obtained the empirical formula of the main cable creep changing with initial stress and time based on the metal time hardening creep theory. Considering the influence of radial shrinkage caused by the creep of the main cable and the aging relaxation of the pre-tightening force of the high-strength bolts, the calculation formula of pre-tightening force loss of the high-strength bolts in the cable clamp of the self-anchored suspension bridge during operation was obtained, and the fine finite element model of integration of the main cable and the cable clamp was established by ANSYS for verification. The verification results show that the solution of the calculation formula is slightly larger than the numerical solution by 10~20kN, and the fitting accuracy is good. Therefore, the empirical formula can provide reference for the detection and reinforcement of the pre-tightening force of suspension bridges.

Cold bending is a new construction method with good application prospects for curved glass curtain wall. To study the mechanical response of cold-bent insulating glass plates, a single curved cold bending experiment was carried out on the insulating glass plates, and the experiment considered the influence of different cold-bent curvatures, glass thicknesses, and cavity thicknesses on the principal stress and inter-layer displacement. Based on the experiment, the finite element numerical simulation of the cold-bent insulating glass plates was carried out. The results show that the principal stress distribution of each surface of the cold-bent insulating glass is uneven；the maximum cold bending principal stress of the glass plate locates on middle point of long side of the convex surface which is most likely to produce damage stress, and the restraint of the spacer bars can cause the displacement of extreme principal stress point on the inner surfaces；the cold bending curvature has the most significant effect on the cold bending principal stress and interlayer displacement of the insulating glass, while the cavity thickness and the glass thickness have smaller effect. The finite element model method and parameters adopted in this study can well simulate the results of the experiment, even though the results is a little conservative. The research results can provide references for the design and construction of single curved cold bend insulating glass.

A new type of joint between concrete-encased concrete-filled steel tubular (CFST) columns and concrete beam was proposed to make wide use of the joint of concrete-filled steel tubular composite column-concrete beam. The tensile force of longitudinal reinforcement at the beam end of the concrete frame was balanced by the ring reinforcement outside the steel tube in the composite column.The longitudinal reinforcement at the beam end was connected with the ring reinforcement in the column in the form of buckle, bending and so on. Six side joints were made and tested under bending monotonic load in order to test the distribution and development of cracks, deformation, failure mode, bearing capacity and ductility of the side joints. And the force transfer mechanism of the anchorage structure of longitudinal reinforcement was revealed. The test results show that, the cracks of the specimens are concentrated in the plastic hinge area at the end of the beam and shows a bending failure mode with sufficient plastic deformation capacity；the ductility coefficient is greater than that of the ordinary reinforced concrete column beam joint；the longitudinal reinforcement at the tensile side of the beam end can yield before the ring bars yield in the column and the specimen reaches the peak load;there is no strain mutation in the longitudinal reinforcement of beam and ring reinforcement of column in the test. The results show that the three connection forms of longitudinal reinforcement and ring reinforcement have similar mechanical performance, and they are all anchored reliably. The test process was simulated by ABAQUS program, which proved the consistence between the calculated results and the test results.

Elevated railway stations are usually large-span buildings and require skylights. Traditional skylight design methods have difficulties in solving the multi-objective problem of complex requirements in lighting and energy-saving. In order to realize the multi-objective optimization of the flat skylight of the high-speed railway station, based on the pre-design parameter settings of the flat skylight of the elevated high-speed railway station, this paper constructed a set of genetic algorithm-based multi-objective optimization methods using Rhino and Grasshopper platforms, building performance simulation tool called Ladybug, and multi-objective optimization tool called Octopus. Multi-objective optimization method for flat skylight goes through the steps of determining variables, determining optimization objectives, building models and programming, using Rhino and Grasshopper to build a simplified parametric model, importing the Ladybug tool for performance analysis, and using Octopus tool to carry out iterative multi-objective optimization according to the analysis results. The optimization process can automatically change and simulate the parameterized part of the model, and record and compare the results of each change and simulation. And finally, it finds out the parameters that best meet the set multiple objectives. Returning the parameters to the parametric model can yield the optimal model and the corresponding building performance simulation results. Furthermore, an empirical analysis was carried out by taking Guangzhou Baiyun Station as an example. According to the requirements of the main lighting standards at home and abroad, the study first set the daylighting factor and the daylighting uniformity up to the standard, the useful daylighting illuminance as significant as possible, the possibility of glare occurrence as small as possible, and the solar radiation as small as possible as the target system. Then it used the method for multi-objective optimization. The results show that compared with the original scheme, the final scheme meets the basic standard of daylighting factor and has better lighting uniformity, useful daylighting illuminance, glare occurrence possibility, and solar radiation under the lighting intensity conditions. The proposed method has a wide range of application scenarios and more flexibility and can provide references for related research.

In order to study the axial compression behavior of a new type of sea water sea-sand concrete circular column reinforced by BFRP longitudinal bars and confined by continuous BFRP spiral strip，also with concrete cover，8 short columns were test under axial compressive load.The influence of reinforcement ratio of BFRP longitu-dinal bars and the width and spacing of BFRP spiral strip on the axial compression performance of the columns was studied.According to the study results，the failure process and mechanism of such new type of column are that the concrete cover cracks and fell off first at middle of its height，then the spiral strips were fractured，finally the core concrete was crushes and the BFRP longitudinal bars are buckling；the damage ranges of concrete covers of the specimens confined by strips are smaller than that of the specimen without strip confining；the BFRP spiral strips can provide some constraint effect on the core concrete and BFRP longitudinal bars and improve the utilization rate of the compressive strength of BFRP bars；the bearing capacity of the new type of column increases with the increase of reinforcement ratio of BFRP longitudinal bars；under the restraint of the strips，the bearing capacity of the specimens is increased by 0.9%~10.4%，and the ultimate displacements is increased by 16.39%~130.82%；reducing the spacing or increasing the width of strips can improve the bearing capacity of the column；the displacement ductility coefficients of the specimens are generally not high.The calculated values from the expression for predicting the axial compression bearing capacity of such column derived in this paper are in good agreement with the experimental values.

This paper carried out axial compression tests on nine circular steel tube confined steel reinforced (CSTCSR) concrete short columns, one circular steel tube confined (CSTC) concrete short column and one circular steel tube column filled with steel-reinforced concrete. The main purpose of this research is to study the influences of yield strength of steel tube and shape steel, diameter-thickness ratio of steel tube, concrete strength, inner surface treatment method of high-strength steel tube and restraint mode on the failure mode, strain response, axial compression bearing capacity and ductility of CSTCSR concrete short column. The results show that the failure mode of high-strength circular steel tube confined high-strength steel reinforced (HCSTCHSR) concrete short column is overall shear failure, and there is no obvious local buckling on the surface of high-strength steel tube, and the development of oblique cracks of concrete is effectively restricted by the embedded high-strength shape steel. For CSTCSR concrete short column, the axial compression bearing capacity ratio and ductility coefficient of this column with high-strength steel tube and high-strength shape steel are increased from 1.37 to 1.49 and from 2.22 to 3.25, respectively, compared with those of CSTCSR concrete short column using ordinary-strength steel tube and ordinary-strength shape steel. It is concluded that the HCSTCHSR concrete short column has more excellent axial bearing capacity and ductility, and high-strength steel using in such column can be fully utilized. On the basis of “technical standard for steel tube confined concrete structures” (JGJ/T471—2019) and the results of parametric analysis in this study, a modified formula for axial bearing capacity of HCSTCHSR concrete short column was proposed by using the existing confined concrete’s constitutive model to provide scientific basis and data support for practical engineering application.

In order to solve the problems of poor anti-interference ability and low recognition accuracy of traditional crack identification algorithms，an image identification system for concrete surface existing cracks was established by improving the existing seed filling algorithm to achieve accurate extraction of crack information.In the pre-processing，the illumination uneven coefficient screening algorithm was proposed to quickly screen the image，which improves the efficiency of uniform light processing.In the crack identification，the existing seed filling algorithm was improved，so that it can automatically determine the growth point of the crack.And the image segmentation of the crack was realized by combining the eight-direction search method with the boundary judgment of the relative threshold method.Then a series of complex background interference were eliminated with the connected domain filter.In the feature extraction stage，by introducing morphological processing，burr removal and node Euclidean distance，the quantitative information of the number of cracks，length and width was accurately obtained.Compared with traditional concrete crack image recognition algorithms，this algorithm achieves a greater degree of unification of efficiency and accuracy，and the extraction error of the crack length and width values is controlled within 10%.

Starting from the critical failure inclined section of reinforced concrete beam without stirrups, this study analyzed the force of each part on the critical failure inclined section. Through theoretical derivation and rational simplification, the value of calculation parameters was obtained, and the calculation model of shear capacity of based on mechanical balance for the reinforced concrete beam without stirrups. On the basis of the classical mechanics principle, the model has a clear physical meaning and can better reflect the influences of shear parameters including concrete strength, shear-span ratio, longitudinal reinforcement ratio and size effect, respectively. Then, the prediction accuracy and stability of the proposed shear model were evaluated based on 9 test specimens by comparing with the GB 50010—2010, ACI 318-14, EC 2, JSCE 2007 and Zsutty calculation formula. Finally, the applicability of the proposed model in the calculation of shear capacity of FRP reinforced concrete beams without stirrups was verified. The results show that the proposed model based on mechanical balance can effectively predict the shear capacity of reinforced concrete beams without stirrups and exhibit the shear failure mechanism of beam oblique section. Moreover, the proposed shear model has a higher prediction accuracy and stability, and can better reflect the nonlinear relationship between shear capacity versus shear-span ratio and longitudinal reinforcement ratio. In addition, the predicted results have a consistent stability with the change of shear parameters, so it can be applied to the shear capacity calculation of FRP reinforced concrete beams without stirrups.