Crack Resistance Capacity Research Articles

Performance enhancement analysis of seismic-damaged RC columns repaired with fiber-reinforced concrete and carbon textile

Repairing seismic-damaged members is an important way to improve the seismic performance of seismic-damaged structures. To effectively improve the seismic performance of seismic-damaged members, this study adopted fiber-reinforced concrete (FRC) and carbon textile for repair. Considering the influences of repair methods, axial compression ratio, and pre-damage degree, six reinforced concrete (RC) columns were designed and manufactured to carry out experimental research. The experimental results showed that using FRC and carbon textile to repair damaged RC columns can improve their failure modes and significantly enhance their mechanical properties, crack resistance, and energy dissipation capacity; Moreover, the relevant displacement-strain curves, displacement-crack width curves, stiffness degradation curves, and damage evolution curves further demonstrated the effectiveness of using FRC and carbon textile for repair. Through theoretical analysis, this study established relevant calculation methods for flexural and shear bearing capacity, and proved the accuracy of the proposed theoretical calculation methods combined with the experimental data. Additionally, the influences of the height of the repaired area, the number of carbon textile layers, and the axial compression ratio on the seismic performance of repaired RC columns are revealed by numerical analysis. The above research can be helpful for the repair of actual seismic-damaged RC columns.

Experimental Study on Pavement Performance of Warm High Modulus Mixture WHMM-13

In order to solve the dusting and rutting problems of hot mix asphalt mixture during construction and operation, rutting test, bending test, Marshall stability test, freeze-thaw splitting test, uniaxial compression dynamic modulus test, overlay test, and four-point bending fatigue life test are applied on WHMM-13 to study the high-temperature stability, low-temperature cracking resistance, water stability, anti-reflection crack performance and fatigue durability in comparison with HMM-13. The results show that, compared to HMM-13, the dynamic stability and dynamic modulus (45 ℃, 10 Hz) of WHMM- 13 are improved by 10.0% and 47% respectively, and the rutting depth is reduced by 27.3%, indicating that the high temperature stability of WHMM-13 has been greatly improved. As for low temperature cracking resistance, the bending failure strain, stiffness modulus, flexural tensile strength and rupture energy of WHMM-13 are slightly lower than those of HMM-13. As for water stability, the residual stability of WHMM-13 in immersion Marshall test is 87.5%, and the splitting strength is 82.3%, both higher than that of HMM-13. As for anti-reflection crack performance, the total tensile rupture energy of WHMM-13 is 2.32 times that of HMM-13, with cracking resistance index (CRI) increased by 25%, which shows that WHMM-13 has better strength, can effectively prevent the crack from spreading and effectively improve the cracking resistance capacity of asphalt pavement. As for fatigue durability, the fatigue life of WHMM-13 is 5.4% lower than that of HMM-13, with bending stiffness modulus and cumulative dissipation energy reduced by 11.3% and 2.8% respectively, indicating that the fatigue durability of WHMM-13 is slightly reduced.

Shear behavior of reinforced concrete beams with high-strength reinforcements after high temperatures

This paper investigates the effect of steel reinforcement configured with different strengths after different high temperatures on the shear performance of the test beams, a total of 20 reinforced concrete (RC) beams, through experiments, numerical analyses and theoretical studies, in order to understand the key factors affecting the shear performance of the beams. The test revealed that the mechanical properties of concrete and steel reinforcement showed a trend of increasing and then decreasing after high temperatures. Increasing the stirrup ratio and stirrup strength can significantly improve the crack resistance and shear capacity of the beams, as well as the deformation performance of the beams. The residual shear strengths of test beams with high-strength stirrups after exposure to high temperatures are significantly greater than those of ordinary reinforced concrete beams. Specifically, the shear capacity of beams with high-strength stirrups after exposure to 800°C increased by 23.7 % compared to ordinary beams, and the mid-span deflection performance increased by 28.7 %. The stresses in the shear span region of the test beams after high temperature were more concentrated at the diagonal and the number of cracks was significantly reduced. In this paper, a simplified formula for calculating the residual shear capacity of RC beams after room and high temperatures is proposed, which can well predict the test results.

Flexural behavior of precast concrete-filled steel tubes connected with high-performance concrete joints

Abstract Precast concrete-filled steel tube (CFST) columns with connection joints are widely used in building structures, yet research on their flexural behavior when connected with various high-performance concrete (HPC) types is limited. This study presents experimental investigations on precast circular CFST columns subjected to flexural loading until failure. These CFST columns, encased in galvanized steel sheets (GSSs), are connected using HPC joints. Two types of HPC joints were tested: an engineered cementitious composite (ECC) and an ultra-high fiber reinforced concrete (UHFRC). Additionally, the study was conducted varying the development length of the reinforcement/concrete filler joint to 150, 200, and 300 mm. Results indicated that increasing the development length of the reinforcement and the connecting concrete joint enhances both the cracking resistance and load-bearing capacity of slender precast CFST columns with an intermediate joint. Moreover, the combination of GSSs with ECC and UHFRC connections enhances the load-bearing capacity, demonstrating performance comparable to that of a typical precast normal concrete control column without an intermediate connection. The experimental results revealed that ECC and UHFRC connections increased the performance by 11 and 17%, respectively, compared to the control column. Additionally, doubling the development length of the ECC joint improved the cracking force, ultimate force, elastic stiffness, and energy absorption by 20, 15, 133, and 64%, respectively, while UHFRC connections showed improvements of 10, 10, 82, and 94%, respectively.

Experimental and Numerical Analysis of Flexural Properties and Mesoscopic Failure Mechanism of Single-Shell Lining Concrete

Despite ongoing research efforts aimed at understanding the structural response of steel fiber reinforced concrete (SFRC), there is very limited research on the failure characteristics and mesoscopic damage mechanism of SFRC, specifically when under flexure. In this study, a four-point bending test of plain concrete (PC) and SFRC with different fiber contents is carried out to investigate the flexural performance of SFRC. The crack propagation process, cracking load, ultimate load, and load-deflection curves of PC and SFRC beams are obtained. Additionally, the discrete element method (DEM), using PFC2D 6.0 software, is adopted to explore the mesoscopic properties of PC and SFRC. The test and simulation results of PC and SFRC beams are compared and analyzed, and some conclusions are drawn. The results show that steel fiber can efficiently improve the compressive strength of concrete when the fiber content is 30 kg/m3, and significantly improve the deformation resistance, crack resistance, and flexural capacity of concrete. The refined numerical models of PC and SFRC beams are established based on compressive strength and aggregate screening results. Through the numerical four-point bending test, the mesoscopic mechanical behaviors of models reveal the damage mechanism of SFRC. The horizontally distributed steel fibers bridge both sides of the cracks to resist crack development, and the vertically distributed steel fibers guide the cracks to the place with strong contact, thus resisting crack height development. The test results show that, for flexural properties, the optimal steel fiber content of SFRC is 31 kg/m3.

Effect of different types of fine aggregates on fatigue resistance and self-healing of fine aggregate asphalt matrices

Fatigue cracking is one of the most common types of distress in asphalt pavements. Each asphalt concrete (AC) constituent and its interactions are relevant to characterize the resistance to fatigue cracking of the ACs. Also, for the selection of materials, it is essential to consider not only the capacity of the material resist to fatigue cracking but also its ability to heal. Materials owning self-heal properties can enlarge the ACs fatigue life. Many former studies investigated the self-healing of bituminous materials at the binder level. However, this material property can be dependent on the binder-aggregate interactions. Thus, the current work aims to evaluate the influence of using different fine aggregates on the fatigue cracking resistance and self-healing capacity behavior of fine aggregate matrices (FAMs). First, granite, basalt, and mica schist aggregates were subjected to physical, morphological, and mineralogical characterization. Then, three FAMs were fabricated with the same asphalt binder and these different fine aggregates. To evaluate the fatigue cracking resistance and self-healing capacity of the FAMs, frequency sweep and time sweep tests were conducted. The simplified viscoelastic continuum damage (S-VECD) theory was used to interpret the results of those tests. The mineral composition of the aggregates impacted the stiffness and the fatigue life of the FAMs. However, there was no significant influence of the aggregates on the self-healing capacity of the FAMs, since there was no significant increase in the fatigue life of the materials after the resting periods in the time sweep tests.

Experimental study and finite element analysis on shear performance of high strength steel reinforced ultra-high performance concrete beam

This paper investigates the shear performance of high strength steel reinforced ultra-high (HSSUHPC). Test were carried out on seven beam specimens with the different parameters of web steel ratio, shear-to-span ratio, and steel fibres content in volume. The failure patterns and load-displacement curves were obtained. The bearing capacity, deformation capacity and strain variation laws of UHPC, steel web, stirrups, tensile longitudinal reinforcement and tensile flange of steel were analyzed. The experimental study established the finite element model of the shear performance of HSSRUHPC beams. The results of finite element fit well with the experimental results. Then parametric analysis was carried out. The results showed two shear failure patterns for the HSSRUHPC beam: shear diagonal compression failure and shear-compression failure. The mechanical process of the HSSRUHPC beam could be divided into four stages: the elastic stage, cracking stage, strengthening stage, and failure stage. There were two peak loads for the load-displacement curves. As the steel ratio of the steel web and yield strength of steel increased, the bearing capacity and deformation capacity of the HSSRUHPC beam increased. The shear-to-span ratio had a significant influence on the failure pattern of HSSRUHPC beam, and with the increase of the shear-to-span ratio, the bearing capacity of the HSSRUHPC beam decreased, but the deformation capacity increased. As fibre content increased, the crack resistance and deformation capacity of the HSSRUHPC beam were improved. With the increasing width ratio between the steel flange and beam, the bearing capacity of HSSRUHPC beam increased, but the change range decreased, so it is suggested that the width ratio between the steel flange and beam should not be larger than 0.6. As the stirrup ratio increased, the bearing capacity of the HSSRUHPC beam increased, but the availability of stirrups decreased, so it is suggested the stirrup ratio should not be over 3 %.

RESEARCH OF THE STRESS-STRAIN STATE OF PRECAST REINFORCED CONCRETE HOLLOW CORE SLABS UNDER THE ACTION OF A CONCENTRATED AND UNIFORMLY DISTRIBUTED LOAD

The scientific work is devoted to a comprehensive study of the stress-strain state of prefabricated hollow-core floor slabs, establishing the nature of deformation, as well as determining the characteristics of crack resistance, deformability and load-bearing capacity experimentally under short-term loads. The experimental data obtained were confirmed by theoretical calculations. The scientific novelty of the experiments carried out within the framework of the presented work lies in the improvement of the principles of direct design of floor slabs from commercially produced beam slabs, the possibility of determining the stress-strain behavior of a slab structure using the formed ends. The method of monitoring the stressed behavior of a slab structure was also further developed. For the first time, the results of full-scale experimental studies of the stress-strain behavior of a prefabricated slab, carried out using the hydraulic loading method, have been obtained, and the features of the deformation of a slab embedded in the wall of a multi-story building have been experimentally established. The article provides recommendations for the practical use of the research results obtained, and also develops technical specifications for the production of concrete slabs during design and construction. The developed proposals were used in the construction of residential buildings in Kharkiv. When using the recommended grade of concrete C25/30 (instead of the actual grade C20/25 tested), the rigidity of the slab increases and its deflections will be smaller. Based on the data obtained from the experimental testing of the slabs, a generally positive test result should be stated. During further serial production of slabs, periodic testing of batches of slabs should be carried out in accordance with DSTU B V.2.6-53:2008. In this case, the slabs are accepted according to the indicators of strength, rigidity, crack resistance, fire resistance limits, frost resistance limits, as well as water resistance of slabs intended for use in aggressive environments. Keywords: concentrated load, testing, concrete, calculation, deflection, transverse force.

Static Bending Mechanical Properties of Prestressed Concrete Composite Slab with Removable Rectangular Steel-Tube Lattice Girders

In recent years, with the development of building technology, the Chinese construction industry has begun to gradually promote the prefabricated buildings to save on construction costs. Among them, composite slabs, as essential components of prefabricated buildings, have been widely used by designers mainly in favor of their low cost. However, is it possible to further reduce the cost without affecting the quality? Researchers think so if the operation cycle of support from the bottom of composite slabs can accelerate and the mechanical properties of their bottom plate can be optimized. To prove this hypothesis, researchers proposed a new type of prestressed concrete composite slab with removable rectangular steel-tube lattice girders (referred to as CDB composite slabs), whose bottom plate consists of a temporary structure composed of a prestressed concrete prefabricated plate and removable rectangular steel-tube lattice girders. Through static bending performance tests on three prefabricated bottom plates and one composite slab, researchers measured corresponding load-displacement curves, load-strain curves, crack development, and distribution, etc. The test results show that the top chord rectangular steel tubes connected to the bottom plate concrete through web reinforcement bars significantly improve the rigidity, crack resistance, and load-bearing capacity of the bottom plate and possess better ductility and out-of-plane stability. The number of supports at the bottom of the bottom plate is effectively reduced, with the maximum unsupported span reaching 4.8 m. Beyond 4.8 m, only one additional support is needed, and the maximum support span can be up to 9.0 m, which provides space for cost reduction. The cooperative load-bearing performance of the prefabricated bottom plate and the post-cast composite layer concrete is good. The top chord rectangular steel tubes are easy to dismantle and can be reused, which reduces the steel consumption by about 24% compared to that used for the same size of ordinary steel-tube lattice-girder concrete composite slabs. It can greatly decrease the cost. In conclusion, the results have shown that the new method researchers proposed here is practically applicable and also provides great space to save on financial costs.

Experimental study on the seismic enhancement of brick masonry spandrels using a single-sided composite reinforced mortar coating

AbstractThe paper reports on four cyclic tests of brick masonry spandrels in reference state and strengthened state. The tests were carried out on full-scale, H-shaped masonry panels to investigate the coupling role of the spandrel in connecting two piers in a historical masonry wall subjected to in-plane lateral actions. Two 250-mm-thick solid-brick masonry samples were tested—one single-leaf, the other two-leaves masonry. Both samples were tested before and after strengthening by applying a Composite Reinforced Mortar (CRM) coating on one surface. The CRM coating consisted of a lime mortar coating (nominal thickness = 30 mm), reinforced with mesh made of Glass Fibre-Reinforced Polymer (GFRP) that was anchored to the wall by GFRP transverse connectors. For the double-leaf masonry, there were additional transverse connectors made of steel bars in concrete cores (artificial diatones) to prevent masonry leaves separation and to improve the bonding of the CRM coating to the masonry. The test responses are compared in terms of crack pattern, failure mode, resistance, displacement and energy dissipation capacity. The tests showed the effectiveness of the proposed CRM system, which increased the spandrel resistance by 33% and 125% in the single—and double-leaf masonry, respectively, with the ultimate drift being 3.2% (one order of magnitude greater than for the unstrengthened reference samples). Data on energy dissipation and the equivalent viscous damping are also collected and compared. Importantly, the presence of the reinforcing mesh and the composite action of the coating and the wall changed the damage evolution and response mechanism, which resulted in a much better seismic response.

Study on the Bending Performance of High-Strength and High-Ductility CRE-Reinforced Concrete Beams

Constant resistance energy (CRE) steel reinforcement has a yield strength of up to 750 MPa and an ultimate elongation of more than 20%. CRE reinforcement overcomes the contradiction between high yield strength and high uniform elongation of ordinary high-strength bars. This paper explores the flexural performance and load-carrying mechanisms of CRE-reinforced concrete beams through a series of experiments, while also presenting a theoretical analytical method for such specimens. Flexural tests on six CRE-reinforced concrete beams and two control tests on hot-rolled ribbed bar 400 (HRB400)-reinforced concrete beams were conducted in this paper. The study examines the influence of the shear–span ratio and reinforcement type on the mechanical response of the beams, including cracking load, yield load, and ultimate load, while analyzing the variation patterns of concrete strain and reinforcement strain. The experimental results demonstrate that as the shear–span ratio decreases, the crack resistance and load-carrying capacity of CRE-reinforced concrete beams improve. Under equivalent conditions, CRE-reinforced concrete beams exhibit higher load-carrying capacity compared to HRB-reinforced concrete beams, surpassing the latter by approximately 43% in terms of ultimate load. Additionally, this paper proposes a calculation method for the mechanical response of NPR-reinforced concrete beams and compares the theoretical values with the experimental values. The differences between the two are within 13%, which proves the reliability of the calculation method.

Elucidation of Static Fracture Energy and Dynamic Tensile Performance of Hybrid Steel Fiber-Based Ultrahigh-Performance Concrete

Ultrahigh-performance concrete (UHPC) has great potential for applications in civil and military structures due to its outstanding performance and ability to withstand impact and blast load. This performance can be attributed mainly to the materials and their proportions, especially metallic fibers. Hence, understanding the behavior of UHPC under static and dynamic conditions through the effect of hybridization of steel fibers is essential. Compressive strength and flexural strength were studied in quasi-static mode. In flexural mode, strain characterization was done using a digital image correlation (DIC) technique. Fracture studies were also conducted with notches using a crack mouth opening displacement (CMOD) technique. In high-strain mode, dynamic tensile strength was evaluated using a split Hopkinson pressure bar (SHPB) with a Brazilian disk. Owing to optimized hybridization, enhancement in (1) toughness, (2) energy absorption, (3) crack-resistance capacity, (4) reserve strength, (5) limit of proportionality, (6) fracture energy, (7) stress intensity factor, (8) tensile strain carrying capacity, and (9) dynamic tensile strength were observed. In the process, other findings in relation to fracture, strain rate, and dynamic increase factor were also exemplified. The SHPB dynamic tensile test results, as well as the technical information provided regarding UHPC’s hybrid steel fibers’ strength, failure, and fracture behavior, can be used to improve the design of UHPC building structures to protect against impact and blast attacks.

Non-destructive testing method of fiber content in steel fiber reinforced concrete based on magnetization loss

Steel fiber reinforced concrete (SFRC) has been widely used in construction engineering due to its superior crack resistance and flexural capacity. Its mechanical properties mainly depend on the distribution of fibers, and the uneven distribution will reduce the structural performance. Therefore, this paper proposed a fast non-destructive testing method for steel fiber content evaluation based on magnetization loss. This method could solve the problem that the traditional methods were difficult to detect in situ. It is found that the higher the steel fiber content, the greater the magnetic loss and electrical loss of the fiber under sinusoidal excitation, resulting in the changes of the excitation coil impedance. Based on this phenomenon, the impedance difference modulus and quality factor evaluation index of the excitation coil are proposed, which can be used to accurately estimate the internal fiber content of concrete in-situ detection. The feasibility of the method is verified by experiments, which is of great significance to the quality control in the manufacturing process of SFRC.

Flexural behavior of RC beams enhanced with carbon textile and fiber reinforced concrete

Concrete cracking is the major cause of steel corrosion and performance degradation of reinforced concrete (RC) members. To significantly enhance the crack resistance and flexural performance of RC beams, textile and fiber-reinforced concrete (FRC) were used in this study, and a simple anchoring method of textile was proposed to prevent debonding failure. Eight RC beams were designed and tested, and the test variables included carbon textile, anchoring method and pouring thickness of FRC. The test results revealed that the proposed anchoring method can effectively avoid the debonding phenomenon; both carbon textile and FRC can improve the crack resistance, improve the flexural capacity and reduce the damage of specimens. Among, the combination of carbon textile and FRC is the most effective method to improve the mechanical properties of specimens. Compared with the ordinary RC beam, the crack resistance and flexural capacity of textile-FRC composite beams can be increased by 79.56% and 39.04% respectively under specific conditions. With the increase of the pouring thickness of FRC, the mechanical properties of the specimens gradually enhanced, while the growth rate gradually slowed down. Through sectional analysis, the calculation methods of the load-midspan deflection curve and flexural capacity of textile-FRC composite beams were established. The accuracy and applicability of the calculation methods were verified by test and finite element analysis. In addition, theoretical calculation results show that the enhancing effect is not significant in the case that the pouring thickness of FRC is beyond 64% of the section height.

Experimental and analytical studies on the flexural behavior of steel plate-UHPC composite strengthened RC beams

In view of the excellent mechanical property of Ultra-High Performance Concrete (UHPC), a new method of using steel plate and UHPC (SP-UHPC) composite to strengthen damaged reinforced concrete (RC) beams was proposed. Four-point bending tests were conducted to investigate the failure modes, deformation characteristics, crack resistance, and bearing capacity of five SP-UHPC strengthened beams (SPUB), one reinforced UHPC strengthened beam (RUB), and one reinforced concrete beam (RCB). Additionally, the impacts of different strengthening techniques, the thickness of steel plate and UHPC on the flexural performance of the strengthened beams were investigated and discussed. The effects of the shear strength of UHPC-RC interface on the bearing capacity of the strengthened beams were analyzed. The test results show that the failure mode of strengthened beams is interface peeling failure. Compared with RCB, the cracking moments of SPUBs and RUB increased by about 214.5%-271.5% and 43.7%, respectively. The bearing capacity of SPUBs and RUB increased by 53.1%-73.7% and 53.4%, respectively. The flexural stiffness of strengthened beams increased by nearly one time on average. Compared with RUB, the SPUBs showed a superior crack resistance and interface slip resistance. The increase in the thickness of the steel plate and UHPC can improve the flexural stiffness and the strain behavior of strengthened beams significantly. Based on the test results, the calculation formulae of UHPC cracking moments and bearing capacity of SP-UHPC strengthened beams were proposed considering the effective anchorage length of interface, the strain hardening behavior of UHPC, and the residual strain in RC beam. The calculation results of UHPC cracking moments and bearing capacity coincide with the test results, demonstrating the accuracy of proposed calculation formulae.

Case Study on Prestressed CFRP Plates Applied for Strengthening Hollow-Section Beam Removed from an Old Bridge.

With the wide application of carbon fiber reinforced polymer (CFRP) plate, used for strengthening existed concrete structures, the prestressing technology of CFRP plate is becoming a hot topic, in order to sufficiently develop its high-strength peculiarity. In this paper, a full-scale hollow-section beam with length of 16 m taken from an old bridge which was in service for about 20 years was first examined for existed cracks and repaired by filling epoxy adhesive, and then the beam was strengthened with prestressed CFRP plates. The CFRP plates were tensioned and fixed with flat-plate anchorages at ends and bonded with adhesive on the bottom surface of the beam. The strengthened beam was experimentally studied using a four-point test to measure the concrete strain along the height of the mid-span section and the mid-span deflection. The finite element model of the strengthened beam was verified by the comparison of test results and used for an extending study of parametric analysis considering the effect of the length and amount of CFRP plates. Results indicated that with an increase in the length and amount of CFRP plates, the mid-span deflection of the beam decreases with the increased cracking resistance and bearing capacity, while the ultimate failure mode transfers from the under-reinforcement to the over-reinforcement.

Tests of reinforced concrete floor slab with initial crack

This study presents the results of the examination of precast reinforced concrete floor slab with initial crack of continuous rectangular cross-section with nominal dimensions 6380*3230 mm and a height of 160 mm. The slab was manufactured in the factory during summer. Concrete curing took place in natural conditions without the use of heat and humidity treatment. The slab has an initial crack that appeared before the test, located in the middle of the span in the direction of the channel-former in the layer of concrete with minimum thickness. Information on the testing procedure is presented, the results of calculations and full-scale tests are given. The analysis of the slab deformation dependence diagram on the load value is carried out. The conformity of crack resistance, stiffness and load-carrying capacity of a slab with an initial crack to the normative requirements has been checked, and the theoretical and experimental results have been compared. The influence of the initial crack in the slab on its stiffness and crack resistance has been established.

Application of Cement-Based Composite Nanomaterials in Prefabricated Thin-Wall Light Steel Structure Composite Wall.

In order to solve the problem of seismic performance of prefabricated concrete shear walls connected with ultra-high performance cement-based composite (UHPC) after short lap of steel bars, the author proposes a cement-based composite nanomaterial in the prefabricated thin-walled lightweight application in steel structure composite wall. In order to explore the influence of the axial compression ratio on its seismic performance, 1 is a cast-in-place shear wall with a design axial compression ratio of 0.2, and 3 is a prefabricated shear wall with a design axial compression ratio of 0.2, 0.33, and 0.47, respectively, all the specimens were mainly damaged by shear compression. The test results show that the cracking loads of specimens PW2 and PW3 are increased by 17.04% and 38.81%, respectively, the yield load is increased by 27.74% and 50.28%, respectively, and the peak load is increased by 25.29% and 48.4%, respectively. Conclusion. With the increase of the axial compression ratio, the crack resistance and bearing capacity of the specimens are significantly improved.

Reinforced Concrete Columns with Local Prestressing Rebars: A Calculation Theory and an Experimental Study

Local prestressing of reinforcement can be effective for slender reinforced concrete columns with large longitudinal force eccentricities. This article deals with columns with prestressed reinforcement on the side opposite to the eccentricity of the longitudinal force. Prestressing is created with the help of turnbuckles. The aim of the work is to develop a model for determining the stress–strain state of columns with local prestress and its experimental verification. The article presents the derivation of a resolving equation for the increment of deflection, which considers the non-linearity of the concrete and reinforcement work, the presence of creep and shrinkage of concrete. The solution of the resulting equation was performed numerically by the finite difference method in a MATLAB environment. Experimental studies were carried out according to the hinged support scheme for eight eccentrically compressed samples, four of which had been prestressed. Experiments and numerical modeling of columns with local prestressing showed a significant increase in crack resistance (by 1.3–2.5 times) and bearing capacity (by 12.5–30%) compared to similar structures without prestressing.

Study on Flexural Behavior of Self-Compacting Concrete Beams with Recycled Aggregates

Currently, numerous studies have focused on the differences in the properties of self-compacting concrete with recycled aggregate (RASCC) and normal concrete (NC), while less attention has been paid to the application of RASCC in reinforced concrete structures. In this paper, four-point bending loading tests were performed on seven RASCC beams and four NC beams, considering the parameter of reinforcement ratio, and the flexural properties were analyzed and compared. The results showed that the failure form, moment–deflection curves, and flexural capacity of the RASCC beams were similar to those of the NC beams. However, the cracking moment and the crack width of the RASCC beams were significantly smaller than that of the NC beams. With an increase in the longitudinal reinforcement ratio, the cracking resistance and flexural capacity of the RASCC beams increased significantly. The cracking moment and flexural capacity could be calculated using the method of the Chinese code GB50010-2010. However, compared with the test values, the predicted deflection was slightly less safe, while the maximum crack width calculation was slightly more conservative. Therefore, the current code formula was revised according to the test results.