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The ultra-high tensile ductility of ECC provides an alternative way to enhance the ductility of structural members by using high-ductile matrix material instead of simply increasing reinforcements. However, the application of ECC members is still limited due to the relatively short research time and the lack of design specifications. Being equivalent to eccentric compressive members, a sectional analysis of RECC columns subjected to combined lateral load and axial compression are proposed in this paper. Based on the design theory of load capacity of eccentric compression columns and the unique constitutive model of ECC, the calculation equations for the sectional load capacity of RECC columns are derived. The analytical prediction of the load capacity of RECC column is evaluated in comparison with that of experiments that confirm the capacity of the proposed calculation method to capture the behavior of the RECC column accurately. The strength-interaction diagrams showing the axial force-moment (N-M) interaction curves are then constructed for analysis using the proposed calculation equations. A parametric study is also carried out by using the proposed calculation equations, demonstrating the effects of ultimate tensile strain of ECC, compressive and tensile strength of ECC, yield strength of steel bar, and reinforcement ratio on the N-M interaction curves of RECC columns. The investigations exhibited in this paper are expected to provide insight into the design principles of RECC columns.

Bolt-ball joints are widely adopted in grid structures due to their high installation accuracy and short construction period. Since the bolt is inside the joint, it is challenging to evaluate its health status from outside the structure. A finite-element plane-truss structure model, based on the actual grid structure, was constructed to investigate the influence of the rod’s preload on the overall stiffness and bearing capacity of the grid structure. Moreover, a model of the grid structure, with a bolt-ball joint connection, was constructed to analyze the influence of the preload loss in bolted-ball joints on the overall mechanical performance of the local members and structures. The results show that the release of preload on the outer web rod is less effective in terms of the overall stiffness and bearing capacity of the structure than on the inner web rod. The preload of the larger span direction rod plays an important role, and the preload of the upper chord has a greater impact, while the preload of the web rod and the upper chord in the smaller span direction has no significant effect on the normal stress in the surrounding rods.

To enhance the durability of a reinforced concrete structure, engineered cementitious composite (ECC), which exhibits high tensile ductility and good crack control ability, is considered a promising alternative to conventional concrete. However, broad application of ECC is hindered by its high cost. This paper presents a new means to address this issue by introducing a composite beam with a U-shaped ECC permanent formwork and infill concrete. The flexural performance of the ECC/RC composite beam has been investigated experimentally with eight specimens. According to the test results, the failure of a composite beam with a U-shaped ECC formwork is initiated by the crushing of compressive concrete rather than debonding, even if the surface between the ECC and the concrete is smooth as-finished. Under the same reinforcement configurations, ECC/RC composite beams exhibit increases in flexural performance in terms of ductility, load-carrying capacity, and damage tolerance compared with the counterpart ordinary RC beam. Furthermore, a theoretical model based on the strip method is proposed to predict the moment-curvature responses of ECC/RC composite beams, and a simplified method based on the equivalent rectangular stress distribution approach has also evolved. The theoretical results are found to be in good agreement with the test data.

Engineered cementitious composite (ECC) is a high-performance composite material with greater shear deformation and shear strength than normal concrete, which has been proposed for use as a shear component in structures. This study modeled three frames, a pure reinforced concrete (RC) frame, an RC frame with concrete short columns and an RC frame with ECC short columns, using the incremental dynamic analysis (IDA) method to evaluate the contribution of ECC to the structural performance. A modified IMK model was applied to model the entire history of the mechanical behaviors of the short columns. The IDA curves, interfloor displacement angle distribution and limit state of the vertex displacement of the frames were analyzed to investigate the seismic responses of the frames. The model analysis results showed that an RC frame with short columns would form a weak layer on the floor where the short columns were located, which greatly weakened the seismic performance of the structure. ECC was certified to be effective in improving the shear formation of the short columns in the frames. The frame with ECC short columns improved the seismic performance of the structure to a certain extent relative to the frame with RC short columns. The deformation capacity of the frame with ECC short columns was close to that of the pure RC frame at the collapse level.

Creep affects the long-term deformation of concrete structures. Nonlinear creep further overestimates the safety factor of structures and affects the safety service performance. The coupling of creep and a damage model considering the rate effect is conducive to accurate prediction of nonlinear creep, but the iterative process of strain makes the calculation method more complex. The purpose of this study is to propose a nonlinear creep explicit method that considers the damage evolution of concrete under compression. Two groups of axial compression members with compressive stresses of 0.2 fc and 0.4 fc were made. Considering the law of concrete damage evolution under uniaxial compression, coupled with elastic creep and damage incremental strain, the lower limit of the medium stress level that gives rise to nonlinear creep is analyzed. The concrete nonlinear creep amplification coefficient with a loading age of 28 days and loading duration of 360 days is studied with consideration for the uncertainty of relative humidity and the theoretical thickness of the component. On this basis, the explicit calculation formula of the nonlinear creep amplification coefficient related to the concrete axial compressive strength and stress level is given. The results indicate that the nonlinear creep amplification coefficient increases nonlinearly with an increase in the stress level, and, when the compressive stress level ratio is higher than 0.6, the nonlinear creep amplification coefficient increases significantly; when the stress level is determined, the creep amplification coefficient decreases gradually with an increase in the compressive strength of the concrete. It is suggested that a stress level range of 0.35~0.75 should be used for the study of a nonlinear creep amplification factor under the medium stress state.

Micromechanics-based models provide powerful tools to predict initiation of ductile fracture in steels. A new criterion is presented herein to study the process of ductile fracture when the effects of both stress triaxiality and shear stress on void growth and coalescence are considered. Finite-element analyses of two different kinds of steel, viz. ASTM A992 and AISI 1045, were carried out to monitor the history of stress and strain states and study the methodology for determining fracture initiation. Both the new model and void growth model (VGM) were calibrated for both kinds of steel and their accuracy for predicting fracture initiation evaluated. The results indicated that both models offer good accuracy for predicting fracture of A992 steel. However, use of the VGM leads to a significant deviation for 1045 steel, while the new model presents good performance for predicting fracture over a wide range of stress triaxiality while capturing the effect of shear stress on fracture initiation.

In modeling necking in steel bars subjected to uniaxial tension using a classical one-dimensional elastoplastic continuum, numerical results exhibit strong mesh dependency without convergence upon mesh refinement. The strain localization and softening with respect to necking in structural steels is induced by hybrid material and geometric nonlinearities rather than material damage. A one-dimensional nonlocal model is proposed to address these numerical difficulties and to provide an enhanced numerical representation of necking-induced localization in structural steels for the potential implementation in fiber-based formulations. By introducing a characteristic length and a nonlocal parameter to the standard constitutive model, the enhanced nonlocal continuum provides a well-posed governing equation for the necking problem. The finite element calculations based on this one-dimensional nonlocal model give rise to objective solutions, i.e., numerical results converge under mesh refinement. In addition, the size of the necking region also exhibits mesh-independence. The characteristic length and nonlocal parameter significantly influence the post-necking response and the dimension of the necked region. Comparison of the local and global response of necking between one-dimensional analysis and 3D simulations demonstrates that the proposed model is capable of accurately characterizing the post-necking behavior. Relationships between characteristic length for the nonlocal model and the diameter of a cylindrical bar are examined. The novel contributions of the paper are: (1) providing a transparent link between the nonlocal formulation and the physics of the necking phenomenon, and (2) providing a mathematical basis for the necessity of the “over-nonlocal” formulation.

This study aims to investigate the shear behavior of reinforced recycled aggregate concrete (RRAC) beams after exposure to elevated temperatures. A total of sixteen 1/3-scale RRAC beams with the shear span-to-depth ratio of 1.2 were tested using the four-point bending facility. The method of equivalent total water was employed to manufacture the RAC. Four recycled coarse aggregate (RCA) replacement ratios (i.e., 0, 30%, 70% and 100%) and three elevated temperatures (i.e., 200 °C, 400 °C and 600 °C) were considered to examine their effects on the shear behavior of RRAC beams. The test results indicate that increasing of the elevated temperatures leads to the change of concrete color from smoky-gray to grayish-reddish and results in reducing the shear performance (i.e., load bearing capacity and initial stiffness) of RRAC beams. The shear damage and mechanism of RRAC beams were similar to those of reinforced natural aggregate concrete (RNAC) beams at the same elevated temperatures. A finite element method developed based on ABAQUS was used to simulate the thermal and shear behavior of RRAC beams. The parametric analysis was then conducted to investigate the effect of transverse reinforcement spacing and shear span-to-depth ratio on the shear behavior of the beam. Six design provisions including GB 50010, ACI 318, Europe 2, BS 8110, AS 3600 and JSCE 15 were employed to evaluate the residual shear capacity of RRAC beams. The evaluation results indicate that the existing provisions derived from RNAC underestimate the residual shear capacity of RRAC beams within the temperature equal to 500 °C.

In recent years, more and more attention has been paid to the grouting material and technology of sleeve connection due to the wide application of prefabricated construction. The performance of sleeve connection, normally determined by the grouting material and technology of sleeves, has a significant influence on the seismic performance of prefabricated concrete structures. This paper presented an experimental study on the mechanical properties of the fiber-reinforced grouting materials and grouted sleeve joints, and the experimental parameters included the fiber type, fiber volume fraction, and fiber length. The main properties of the grouting materials were investigated, including fluidity, compressive strength, and flexural strength. The test results showed that the incorporation of fibers with different types, volume fractions, and lengths had different effects on the mechanical properties of the grouting material. Based on the grouting material tests, the sleeve splice test was conducted to investigate the influence of different anchorage lengths on the sleeve splice under the uniaxial loading, which indicated that substantial improvement could be observed for the mechanical properties and residual bond strength of the splices with fiber-reinforced grouting materials.

Strain-hardening cementitious composite (SHCC) is a kind of construction material that exhibits multiple cracking and strain-hardening behaviors. The partial replacement of cement with fly ash is beneficial to the formation of the tensile strain-hardening property of SHCC, the increase of environmental greenness, and the decrease of hydration heat, as well as the material cost. This study aimed to develop a sustainable construction material using a high dosage of fly ash (no less than 70% of the binder material by weight). Based on the micromechanics analysis and particle size distribution (PSD) optimization, six mixes with different fly ash to cement ratios (2.4&ndash, 4.4) were designed. The mechanical properties of the developed high-volume fly ash SHCCs (HVFA-SHCCs) were investigated through tensile tests, compressive tests, and flexural tests. Test results showed that all specimens exhibited multiple cracking and strain-hardening behaviors under tension or bending, and the compressive strength of the designed mixes exceeded 30MPa at 28 days, which is suitable for structural applications. Fly ash proved to be beneficial in the improvement of tensile and flexural ductility, but an extremely high volume of fly ash can provide only limited improvement. The HVFA-SHCC mix FA3.2 (with fly ash to binder ratio of about 76% by weight) designed in this study is suggested for structural applications.

A uniaxial cyclic constitutive model for strain-hardening cementitious composites (SHCCs) is proposed based on the response of the material at the stress–strain level under different loading regimes. The ascending branch of the compressive envelope curve was developed using the form of a parabolic curve, while the descending branch adopted the bilinear form. The full tensile stress–strain curve was approximately simulated by a trilinear form comprising ascending, strain-hardening and descending branches. Using the method of setting a reference point, the characteristics of the unloading and reloading process were determined, with consideration of the partial unloading–reloading scheme. Furthermore, the transition between tension and compression was taken into account in the model development. The proposed cyclic constitutive model was coded into the OpenSees platform and applied to simulate the responses of specimens at material and member levels. The simulation results indicate that the proposed model is reasonably accurate in simulating the mechanical properties of SHCC material and the cyclic behaviour of SHCC flexural elements.

Most of the existing prediction models for creep and shrinkage are established based on the statistical regression analysis of test data drawn mostly from experiments performed on normal-strength concrete, and they might not be as applicable to high-strength high-performance concrete. The prediction precision can be improved by carrying out on the given concrete short-term creep and shrinkage measurements. A three-level experimental approach for creep and shrinkage is proposed in this study. Take the high-strength high-performance concrete used in the auxiliary shipping channel bridge of Sutong Bridge for example, the detailed three-level experimental process and results were presented. The specimens were grouped on three levels: “Material level”, “Component level” and “Structural level”. On the first level, plain concrete specimens were experimented in a constant temperature and constant humidity room. On the second level, creep and shrinkage of reinforced concrete specimens with different reinforcement ratio were experimented. On the third level, the long-term behavior of a segmental concrete cantilever beam, 12.8 m long, under natural environment which was close to that of the actual bridge was studied. This experimental approach can provide a new train of thought to improve the predicted precision of the creep and shrinkage effects of the long-span concrete structures.

Steel fiber-reinforced prestressed concrete (SFRPSC) members typically have high shear strength and deformation capability, compared to conventional prestressed concrete (PSC) members, due to the resistance provided by steel fibers at the crack surface after the onset of diagonal cracking. In this study, shear tests were conducted on the SFRPSC members with the test variables of concrete compressive strength, fiber volume fraction, and prestressing force level. Their localized behavior around the critical shear cracks was measured by a non-contact image-based displacement measurement system, and thus their shear deformation was thoroughly investigated. The tested SFRPSC members showed higher shear strengths as the concrete compressive strength or the level of prestress increased, and their stiffnesses did not change significantly, even after diagonal cracking due to the resistance of steel fibers. As the level of prestress increased, the shear deformation was contributed by the crack opening displacement more than the slip displacement. In addition, the local displacements around the shear crack progressed toward directions that differ from those expected by the principal strain angles that can be typically obtained from the average strains of the concrete element. Thus, this localized deformation characteristics around the shear cracks should be considered when measuring the local deformation of concrete elements near discrete cracks or when calculating the local stresses.

There is growing interest in the development of earthquake resilient structures. This paper proposes a new kind of self-centering post-tensioned precast beam-to-column connection, assembled using unbonded posttensioning strands, and steel top and seat angles (PTSA). A series of cyclic loading tests along with numerical simulations were performed to investigate the seismic behavior of the PTSA connection. In the experimental tests, eight subassembly specimens were prepared with varying specimen parameters including the initial posttensioned force, beam depth, and type of steel angles. Test results show that the properly designed specimens had large initial stiffness, good recentering capacity, and high ductility. Permanent deformation was concentrated in the steel angles, which were relatively easy to replace. Precast beams, columns, and PT strands in each subassembly behaved almost elastically up to 3.5% drift. Additional tests on a previously tested PTSA specimen with newly replaced steel angles demonstrated that the cyclic responses were almost identical to the original counterpart. Numerical analyses were carried out using the platform OpenSees to examine the effects of the concrete initial compressive stress, the initial prestress, the concrete compressive strength, and the beam cross-sectional width on the mechanical response of PTSA. Results indicate that appropriate areas and initial prestress of the PT strands, and concrete compressive strength were beneficial to the load-carrying and deformation capacities of PTSA. Increasing the beam cross-sectional width may improve the ductility of PTSA.

The effect of hybrid CaO- and ettringite-based expansive agents (HCSA) on the mechanical properties and durability of shrinkage-compensating concrete (SHRCC) is not well established. In this paper, SHRCC specimens were prepared incorporating with a high-performance calcium sulfoaluminate- hydrate calcium hydroxide expansive agent (HCSA) and three different types of fibers, i.e., polypropylene fiber (PP), polyvinyl alcohol fiber (PVA), and cellulose fiber (CF). The first part of the experimental program included material tests of the slump, compressive strength, restrained expansion ratio, early crack resistance, permeability and chloride penetration of SHRCC. The test results indicated that the HCSA-based SHRCC exhibited good workability, early crack resistance and durability. It is suggested that HCSA with a dosage of 7% − 8% of the weight of binder materials provided favorable shrinkage compensation and early crack resistance and had negligible impacts on the slump and compressive strength of the SHRCC. Although the content was low (approximately 0.7% by volume), PP fibers effectively improved the early crack resistance of the SHRCC. Adequate moist curing was also required to retain acceptable permeability and chloride penetration of the SHRCC. The second part of the experimental program involved tests on small-scale concrete basement slabs, which verified the effects of the expansive agent and fibers on the crack resistance of SHRCC at the component level.

This paper presented a new kind of steel-reinforced engineered cementitious composite (RECC/C) columns, which consisted of a permanent formwork fabricated by the steel-reinforced ECC (RECC) and plain concrete infilled within the RECC formwork. The main objective of this paper was to examine the seismic behavior of the RECC/C columns through experimental and numerical approaches. Six RECC/C composite columns and a corresponding conventional reinforced concrete (RC) column specimen were prepared for the experimental investigations. The test results revealed that the RECC/C composite columns had better shear capacity, energy dissipation capacity, and a higher ductility as compared to the RC column. An increase in the transverse reinforcement, shear-span ratio, or a decrease in the axial compression resulted in the improvement of the ductility and energy dissipation capacity of the RECC/C columns. Numerical modeling of the RECC/C column was carried out based on OpenSees. The parametric studies offered insights into the effects of the longitudinal reinforcement, shear-span ratio, axial compression, ECC compressive strength and ultimate compressive strain, and the thickness of ECC layer/formwork on the flexural behavior of the RECC/C columns. The results showed that an increase in each of those ECC material parameters may be beneficial for the member ductility. An appropriate thickness of the ECC layer was crucial to the flexural behavior of the proposed composite columns.

Engineered Cementitious Composites (ECC) is a typical High Performance Fiber Reinforced Cement-based Composite (HPFRCC), which possesses the characteristics of ultra-high tensile ductility and energy dissipation capacity. One of the potential applications of ECC is to replace conventional concrete in the seismic resistant structures. However, to date, the investigation on seismic performance of ECC at the structural level is still limited. This paper aims at evaluating the seismic performance of RECC frame on the basis of Performance-based Seismic Design (PBSD) concept and discussing the feasibility and practicability of applying ECC in structures for improving the seismic performance. The non-linear behavior of ECC material was simulated especially considering the strain hardening behavior in tension. By using the Incremental Dynamic Analysis (IDA) method, three types of frames, consisting of a normal RC frame, a RECC frame and an RECC/RC composite frame, were analyzed to evaluate the structural dynamic behavior of the frames. Comparative studies on the deformation limit states at five levels of seismic performance for these three different types of frames validated that RECC frames have superior deformation capacity comparing to traditional RC frames under high intensity earthquake. Comparison results also indicated that rationally applying ECC in key region of the structures can not only improve the seismic performance and deformation capacity of structures but also control the construction cost.

In this study, shear tests on steel fiber reinforced-prestressed concrete (SFR-PSC) members were conducted with test parameters of the concrete compressive strength, the volume fraction of steel fibers, and the level of effective prestress. The SFR-PSC members showed higher shear strengths and stiffness after diagonal cracking compared to the conventional prestressed concrete (PSC) members without steel fibers. In addition, their shear deformational behavior was measured using the image-based non-contact displacement measurement system, which was then compared to the results of nonlinear finite element analyses (NLFEA). In the NLFEA proposed in this study, a bi-axial tensile behavior model, which can reflect the tensile behavior of the steel fiber-reinforced concrete (SFRC) in a simple manner, was introduced into the smeared crack truss model. The NLFEA model proposed in this study provided a good estimation of shear behavior of the SFRPSC members, such as the stiffness, strengths, and failure modes, reflecting the effect of the key influential factors.

An experimental investigation was carried out to examine the seismic behaviour of three lightly reinforced concrete walls with openings subjected to reversed cyclic loading. The three specimens consisted of one solid wall as the control specimen while the other two walls were detailed with regular or irregular openings. The test results indicate that all three specimens eventually failed when the outermost reinforcing bars fractured while the concrete in the compression zone crushed and spalled severely near the base. The specimen with five openings had ultimate strength and stiffness degradation similar to the control specimen. The specimen with nine openings had a lower ultimate strength but exhibited higher ductility, slower stiffness degradation and a more significant shear contribution than the control specimen. Furthermore, strut-and-tie models were developed to predict the ultimate strength of walls with openings. The results obtained from the strut-and-tie models were found to be consistent with the experimentally observed results.

Engineered cementitious composites (ECC) which shows prominent tensile ductility and toughness, and fine multiple cracking, meets the high requirements of safety and durability in developing sustainable infrastructures. Currently, the cost of oiled polyvinyl alcohol (PVA) fiber widely used in ECC is very high. The price of regular unoiled PVA fiber is relatively lower, however, the tensile ductility of unoiled PVA-ECC may be limited. Based upon the micromechanics model, the feasibility of use of unoiled PVA fibers and hybrid PVA fibers in ECC were studied, and the mix proportion was redesigned through parametric analysis. The four-point bending test, uniaxial tensile test and uniaxial compressive test were carried out to characterize the mechanical behavior of ECC with 21 mix proportions. According to the cost and performance of PVA-ECC, three typical mixes were proposed: M7 with low cost, relatively low tensile ductility and reinforced by unoiled PVA fibers, M17 with moderate cost, relatively high tensile ductility and reinforced by hybrid PVA fibers and M21 with high cost, high tensile ductility and reinforced by oiled PVA fibers. In practical applications, the determination of mix depends on the structural performance requirements.

This article describes an experimental study carried out on of reinforced concrete (RC) walls of less confining reinforcement than that recommended by ACI 318. A total of eight RC walls with boundary elements comprising of five walls with aspect ratio of 1.125 and three walls with aspect ratio of 1.625 were tested by subjecting them to low levels of axial compression loading and simulated seismic loading, to examine the structural performance of the walls with limited transverse reinforcement. Conclusions are reached concerning the failure mode, drift capacity, strength capacity, components of top deformation, and energy dissipation characteristics of walls on the seismic behavior with limited transverse reinforcement. The influences of axial loading, transverse reinforcement in the wall boundary elements, and the presence of construction joints at the wall base on the seismic behavior of walls are also studied in this paper. Lastly, reasonable strut-and-tie models are developed to help in understanding t...

Grouted sleeve connectors provide a convenient and economical solution for connecting precast concrete elements in engineering site. However, sleeve connections may include insufficient grouting defects at certain conditions which may significantly decrease the bearing capacity and increase the failure risk of connection joints. In order to better understand the influence of insufficient grouting defects, the mechanical performance of insufficiently grouted sleeve connections with predesigned vertical grouting defects is investigated in this study by considering three loadings: uniaxial tensile loading, cyclic loading at high stress and cyclic loading at large strain. Comparatively, the repaired sleeve connections by refilling grout material to the sleeve enclosing insufficient grout material are considered as well. Total 24 sleeve connection specimens are tested and the correlation of failure mode, force-displacement response and the defect level is analyzed and discussed. It is revealed that the failure mode of defective specimens may shift from the tensile fracture of reinforcing steel bar to the interfacial bond-slip failure of rebar with the decrease of the anchorage length of reinforcing steel bar. Additionally, it is found that the loading condition affects the failure mode too. Moreover, the repaired sleeve connections show similar mechanical performance to the fully grouted sleeve connection except deformation. This indicates that the regrouting operation to repair the grouting defect in the sleeve is effective in engineering applications.

This paper employs a micromechanics framework to investigate the mechanisms and to predict the ductile fracture of structural steels at intermediate and low-stress triaxialities and under shear involved stress states. Unit cell-based micromechanical analyses are carried out to provide insights into the combined effects of triaxiality, Lode parameter, and shear stress component on the micro-mechanisms of ductile fracture. Based on the micromechanical analyses, an existing fracture model is modified to incorporate the influence of the shear stress component. Experimental investigations are carried out on three axisymmetric tension specimens, and a series of shear specimens made of Chinese Q460 steels to achieve uniaxial tension and shear dominated loading conditions, respectively. Finite element analyses are performed to evaluate the stress and strain fields in the tension and shear specimens. The modified model is calibrated by combining the experimental results with micromechanical analyses. Validation studies show that the predicted fracture initiation by the model agrees well with experimental results, implying a good performance of the proposed micromechanics framework for the prediction of the shear-dominated ductile fracture at intermediate and low-stress triaxialities.

Beam deflections in cases of diagonal and bending cracking of reinforced concrete (RC) beams can be attributed equally to shear and flexural deformations. However, the extent of contribution by shear deformation is hard to quantify and is often underestimated in practical design. To address this, a quantitative analysis of the effect of shear deformation was conducted, considering the effect of tension stiffening after diagonal cracking, and a formula to derive effective shear stiffness is proposed. Five RC beams, comprising of three RC T-section beams with thin web and two RC rectangular beams, were tested to verify the theoretical models with minimum crack angle and total deflection as key points of comparison. The fully cracked responses were analyzed using truss model analogies while exact models applied depended on the crack angle. Results show that shear contribution to the total deflection in the diagonally cracked RC beam is significant.

This paper seeks to examine the concrete contribution to shear strength and determine the inclination of the compressive strut within the variable truss model for slender RC shear-critical beams with stirrups. Using the modified compression field theory in place of the conventional statistical regression of experimental data, the expression for the concrete contribution to shear strength was derived, and the inclination of compressive struts was determined. A simplified explicit expression for shear strength was then provided, with which shear strength can be calculated without extensive iterative computations. This method was then verified using the available experimental data of 209 RC rectangular beams with stirrups and compared with the current methods from the American Concrete Institute and the Canadian Standards Association. The theoretical results are shown to be consistent with the experimentally observed behavior of shear-critical RC beams.

Experimental observations on 11 Reinforced Concrete (RC) columns tested at Nanyang Technological University (NTU), and existing experimental data of 79 shear-critical RC columns are presented. Significant arch action is found in columns of small shear span-to-depth ratio and high axial-load ratio under shear force. Utilizing the sectional method for shear strength of these types of columns, which does not consider arch action, would give a more conservative prediction. Based on the truss-arch model, an expression to predict the shear strength of shear-critical RC columns is presented, which considers both the contributions of concrete and transverse reinforcement to shear strength in the truss model as well as the contribution of arch action through compatibility of deformation. The proposed model is compared with other shear strength models using the available column test data consisting of 90 shear-critical RC columns, and the results show that the proposed model can improve the accuracy of shear strength predictions for shear-critical RC columns Accepted version

The seismic performance of steel reinforced engineered cementitious composite (RECC) short columns was investigated in this study. RECC columns with various shear span-to-depth ratios, axial load levels and transverse reinforcement ratios, together with one control reinforced concrete (RC) short column, were tested under the combined action of constant axial loading and reversed cyclic lateral loading. Test results indicate that RECC columns are superior to RC columns in terms of ductility, energy dissipation capacity and damage tolerance. The control RC column and the RECC column with the smallest shear span-to-depth ratio (of 1.42) were found to fail in shear. All other RECC columns, with higher shear span-to-depth ratios, including one RECC column without stirrups, failed in a flexure-dominated manner. Furthermore, theoretical flexural strength and shear strength expressions of RECC columns were derived and validated by the test results.

Adjacent precast, prestressed multibeam bridges have often been used for medium- and short-span bridges. However, there have been longitudinal cracking problems in shear keys and overlays commonly seen on some adjacent precast multibeam bridges during their service years. The fundamental reason for the problem is the poor transverse connection. Transverse posttensioning is important to the transverse connection design, although the posttensioning varies largely from state to state. Especially for adjacent precast solid multibeam bridges without diaphragms, there are no theoretical justifications for designing the transverse posttensioning. In this study, an approach based on the concept of shear friction, which is used for designing the transverse posttensioning in adjacent precast solid multibeam bridges, is presented. Furthermore, a newly rehabilitated bridge was load tested with the primary purpose of evaluating the effect of transverse posttensioning under truck load. Also, the calibration of a numerical model was conducted. At last, suggestions about design and construction of shear keys, with reference to the experience in other states, are presented for the practice in the state of Maryland.

It is important to accurately estimate creep and shrinkage effects in long-span continuous box girder bridges. Based on the experiments on creep and shrinkage of the plain concrete used in the continuous rigid frame of Sutong Bridge, China, the applicability of ACI 209–82, JTG D62–2004, B3 and GL2000 prediction model for creep and shrinkage on the high-strength concrete is evaluated. Also, a modified model based upon JTG D62–2004 is presented. Results indicate that the accuracy of prediction of creep and shrinkage can be enhanced greatly by carrying out short-term creep and shrinkage measurements on the given concrete and modifying the prediction model parameters accordingly. Furthermore, the presence of steels can have an impact on the time-dependent deformations caused by creep and shrinkage, accordingly, the restraint influence of steels on creep and shrinkage is investigated through the reinforced specimens with different reinforcement ratio. Formulas of influence coefficients of steels on creep and shrinkage are derived, and a good agreement is observed between the calculated values of the influence coefficients of steels on creep and shrinkage and the measured data in each specimen. The reinforced specimens can be also used for calibrating the modified model.

The long-term behavior of long-span prestressed concrete continuous rigid-frame bridges is significantly sensitive to creep and shrinkage. Therefore, it is important to accurately estimate creep and shrinkage effects. This paper presents modified prediction models that are based on creep and shrinkage models in the existing bridge code. These modified prediction models match well with the test results of the high-strength concrete used in the continuous rigid frame of the Sutong Bridge in China. Results indicate that the accuracy in predicting creep and shrinkage can be enhanced greatly by measuring short-term creep and shrinkage on the given concrete and by modifying the prediction model parameters accordingly. Subsequently, the probabilistic analysis method of structural creep and shrinkage effects was studied. Uncertainty analysis of time-dependent effects in the given bridge was performed using the modified model, and results were compared with field-test data. Two approaches for mitigating deflections used in the continuous rigid frame of the Sutong Bridge are introduced. Finally, the time-dependent deflection at the midspan attributable to creep and shrinkage was analyzed.

An experimental investigation has been conducted to examine the seismic behavior of seven shear-critical, high-strength concrete columns and one normal-strength concrete column. The effects...

Excessive deflections unexpected at the midspan have commonly appeared in long-span prestressed concrete box girder bridges, mainly because of the high degree of uncertainty in concrete creep and shrinkage, prestress loss, and variations in the environment. Arrangement of backup prestressing tendons that will be tensioned based on deflection development during the service years is an effective solution to this problem. First, an uncertainty analysis of the long-term deformation at the midspan of a bridge was performed using the Latin hypercube sampling method, with the consideration of model uncertainty of creep and shrinkage and random properties of influencing factors; consequently, the 95% confidence interval of the deformation at the midspan was determined. Then, a quantitative design of backup tendons was performed on the basis of the difference between the lower limit and mean value of the 95% confidence interval of deformation. Lastly, the efficiencies of different arrangement schemes of backup tendons were compared, and results show that arrangement of combined external tendons along the girder is the most effective measure for control of long-term deflection.