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This study presented an experimental investigation on the degradation of mechanical performance of reinforced concrete (RC) columns with the reinforcements corroded under sustained loads. A total of ten RC column specimens were tested. The effects of different levels of sustained load (0%, 30%, and 60% of the designed ultimate bearing capacity Nu) and reinforcement corrosion (0%, 5%, 10%, and 20%) on the failure modes, ultimate bearing capacity, and axial load–axial deformation relationship were analyzed. The results showed that the coupling adverse effects due to the reinforcement corrosion and sustained load considerably exacerbate the mechanical deterioration of RC columns and turn the failure mode into a much more brittle manner. Compared with the control specimen L-0-0, the ultimate bearing capacity of the specimen L-4-20 could be reduced as much as about 42%. Based on the test results, an improved model was proposed to estimate the ultimate bearing capacity of corroded RC columns, in which the effects of the corrosion of both longitudinal reinforcements and stirrups and the corrosion-induced spalling of concrete cover were taken into consideration. The close agreements between the analytical predictions and test results prove the applicability of the model. [ABSTRACT FROM AUTHOR]

With an extension in service years, bridges inevitably suffer from performance deterioration. Columns are the main components of bridge structures, which support the superstructure. The damage of pier columns is often more harmful to bridges than that of other components. To accurately evaluate the time-varying characteristics of corroded columns, this paper proposes a new model for the bearing capacity evaluation of deteriorated reinforced concrete (RC) eccentric compression columns based on the Hermite interpolation and Fourier function. Firstly, the axial compression point, the pure bending point and the balanced failure point were selected as the basic points, and the deteriorated strength of these basic points was calculated by considering factors such as concrete cracking, reduction of reinforcement area, buckling of the steel bar, bond slip and strength reduction of confined concrete. After that, the interpolation points were generated by a piecewise cubic Hermite interpolating polynomial, and the explicit expression of the interpolation points fitting function was realized by the trigonometric Fourier series model. Finally, comparison studies based on measured data from forty-five corroded RC eccentric compression columns were conducted to investigate the accuracy and efficiency of the proposed method. The results show that: (1) the prediction results for bearing capacity of corroded RC columns are in good agreement with the measured data, with the average ratio of predicted results to test results at 1.06 and the standard deviation at 0.14; (2) the proposed model unifies the three stress states of axial compression, eccentric compression and pure bending, and is consistent with the continuum mechanics characteristics; (3) the decrements of axial load carrying capacity for 10% and 50% of the corrosion rate are 31.4% and 45.2%, while in flexure they are 25.4% and 77.4%, respectively; and (4) the test data of small-scale specimens may overestimate the negative effect of corrosion on the bearing capacity of actual structures. The findings in this paper could lay a solid starting point for structural life prediction technologies based on nondestructive testing. [ABSTRACT FROM AUTHOR]

Summary: The objective of this contribution is to present some new recent developments regarding the evaluation of the ultimate bearing capacity of massive three‐dimensional reinforced concrete structures which cannot be modeled as 1D (beams) or 2D (plates) structural members. The approach is based upon the implementation of the lower bound static approach of yield design through a discretization of the three‐dimensional structure into tetrahedral finite elements, on the one hand, the formulation of the corresponding optimization problem in the context of semi‐definite programming techniques, on the other hand. Another key feature of the method lies in the treatment of the concrete‐embedded reinforcing bars not as individual elements, but by resorting to an extension of the yield design homogenization approach. The whole procedure is first validated on the rather simple illustrative problem of a uniformly loaded simply supported beam, then applied to the design of a bridge pier cap taken as an example of more complex and realistic structure. [ABSTRACT FROM AUTHOR]

This paper aims at contributing to a better understanding of the physical-mechanical behaviour of partially loaded areas in reinforced concrete. Following a review of the current state of the art on this topic, which includes a description of the mechanical behaviour and existing predictive models, a remarkable knowledge gap in this standard problem is revealed. A new stress field solution for reinforced concrete blocks under strip loading is developed herein which is based on the lower-bound theorem of limit analysis and adopts a modified Coulomb failure criterion for concrete. Contrary to existing empirical design rules, the new mechanical model consistently accounts for the behaviour of concrete under multiaxial compression as well as the favourable effect of transverse reinforcement. While a comparison of the ultimate loads predicted using the new stress field solution shows a good correlation with the available test data, further experiments are required particularly for the validation of the predicted higher resistances of heavily confined areas as compared to existing design rules. [ABSTRACT FROM AUTHOR]

With the increasing threat of terrorism attack, the probability of explosion inside the subway is very large. Reinforced concrete columns are the main supporting members of subway stations. If the columns of a subway station were subjected to near-field explosions, their damages can affect the safety of the subway after explosion. By using the finite element method, this paper established a coupling 'explosive-air-concrete' model and verified the feasibility of the model through experiments. This model can be used in the damage assessment of subway station columns in terms of the bearing capacity, by which the damage of a reinforced concrete column can be divided into different levels. Furthermore, the effect of different parameters on the damage and bearing capacity of the subway station is discussed. The results demonstrate that the stirrup reinforcement ratio of a reinforced concrete is the key factor in determining the column damage under blast loadings. The present study therefore provides a key reference for assessing the damage of subway structures after terrorist attack. [ABSTRACT FROM AUTHOR]

The experimental results on the effectiveness of patch repair and FRP bonded laminates to retrofit reinforced concrete beams with corrosion damage are discussed in this paper. The uncovering of the damaged concrete cover provides a more accurate assessment of the corrosion degree, as the actual mass loss of reinforcement can be better calibrated. The mass loss of the tensile reinforcement varied at approximately 7.5%–24%. The necessity of the removal of the cracked concrete substrate, treatment of corroded reinforcement and repair by patching with a polymer modified mortar is highlighted. Two different strengthening techniques are implemented, of externally bonded EBR or NSM Carbon FRP laminates, having equivalent axial rigidity. CFRP wraps were also applied for shear strengthening to replace corroded stirrups. The load-deflection curves showed that the effect of corrosion on load bearing capacity and bond between the concrete and steel was detrimental for high mass losses. A satisfactory force transfer through the old and patch repaired concrete and through repair mortar and CFRP reinforcement interface was noted. The shear strengthening not only prevented the debonding of the EB laminate at the end but also improved the bond performance between the laminate and concrete, especially for the high corroded beam. [ABSTRACT FROM AUTHOR]

This paper presents an experimental program performed to investigate the behavioral characteristics of unbonded steel-reinforced laminated elastomeric bearings (U-SLEBs), which have been widely used for highway bridges in China. The influences on the friction behaviors, stiffness, and energy dissipations of the different parameters, such as compressive stresses, loading rates, and rubber material, were discussed. The responses of the U-SLEBs were compared with those of the bonded steel-reinforced laminated elastomeric bearings (B-SLEBs). Then, effective analytical models were developed, which considered the mechanical degradation of the U-SLEBs and simulated the realistic behaviors of the B-SLEBs. The seismic responses of a multispan continuous bridge with tested bearing components were also evaluated. The results showed that the mechanical properties of the U-SLEBs tended to degrade due to friction sliding. However, the degrees of the decrease were found to be dependent on the influencing parameters. Meanwhile, the B-SLEBs exhibited stiffening behaviors that led to tearing under large displacement demands. The bridges using U-SLEBs were found to suffer less damage due to the reliable sliding behavior of U-SLEBs. It is recommended that shear keys, which are reasonably designed in the transverse direction, be constructed in order to achieve better seismic performance. [ABSTRACT FROM AUTHOR]

This paper deals with the modeling of the load test of vertical resistance of reinforced concrete piles. The pile is a part of a group of piles with reinforced concrete heads. The head is pressed with steel arches of a bridge on highway Jablonov - Studenec. Pile model is created in ANSYS with several models of foundation having properties found out from geotechnical survey. Finally some crucial results obtained from computer models are presented and compared with these obtained from experiment. [ABSTRACT FROM AUTHOR]

Knife-edge bearing of railway bridges on steel sheet pilings Generally, the infrastructure of railway systems in Austria is considered as adequate. The main issue is the renewal or maintenance of existing structures. Especially railway bridges are planned as substitutional reconstructions of existing routes. Usually, such interventions at existing systems have a significant impact on the rail traffic, leading to relevant economic forfeits in most cases. For this reason it is a recurring challenge for planners of such substitutional reconstructions to minimize the restrictions for the railway traffic. Supported by the ÖBB and in collaboration with the Institute of Structural Concrete of the TU Graz, the planning office Schimetta Consult ZT GmbH investigated on an alternative approach to this problem where the temporary steel sheet pilings are integrated to the reinforced concrete superstructure as permanent structural members. The investigations are limited to the feasibility study of knife-edge bearing of small railway bridges on steel sheet pilings. It was shown that dealing with such small bridges the implementation of this method represents a very interesting alternative to the conventional ones. [ABSTRACT FROM AUTHOR]

Steel reinforced concrete column has been widely applied in high-rise buildings and long-span structures. In this paper, an analytical study is carried out for predicting the axial compressive behavior of steel reinforced concrete (SRC) column using cross-shaped steel section with flanges. Firstly, respective material models were established for different components in the composite cross-section, including highly confined concrete, partially confined concrete, unconfined concrete, steel section as well as steel reinforcement. For highly confined concrete, the interaction mechanism between steel section and confined concrete has been investigated, based on which a uniaxial stress-strain relation is established. For partially confined concrete, as the hoop may not yield, an iterative procedure is applied to calculate the real stress in hoops and then the effective lateral confining pressure. For steel section, the biaxial stress state is considered in the material model. Based on section analysis method, a unified analytical model is then proposed and verified through comparison of analytical results with test results on SRC and partially confined SRC (PSRC) short columns. At last, a simplified method for calculating the real stress of the hoop and then the strength of partially confined concrete was proposed to avoid the iterative process and save the computing time. [ABSTRACT FROM AUTHOR]

Reinforced soil is a composite material in which elements of high tensile resistance are implemented to increase the tensile resistance of the soil. Geotextiles are one of the major groups of geosynthetic products that are used for soil reinforcement. This paper deals with the effects of using nonwoven geotextile to improve the ultimate bearing capacity of footings resting on sand with medium density. The plate load tests were performed using 27 cm × 27 cm and 35 cm × 35 cm square plates, and the effects of the depth of the first layer of geotextile, vertical spacing as well as the number of geotextile layers on the ultimate bearing capacity of the footings were studied. Moreover, the impact of plate size and sample size was examined numerically by performing 3-D finite element analyses with different sizes of the square plate. The experimental results showed that the maximum bearing capacity is achieved for the system with four geotextile layers, vertical spacing of 0.3 B between geotextile layers and geotextile width of 4 B, where B is the width of the plate. The numerical analyses indicated that with increasing the size of the plate up to 65 cm, the values of the bearing capacity ratio (BCR) gradually decrease; however, additional increase in the size of the plate has a little impact on BCR values. [ABSTRACT FROM AUTHOR]

A large number of old bridges are to be found on highways and roads all around the world. Considering their age and deterioration level, many of them need to be reconstructed. However, in the majority of cases, the load-bearing capacity of such bridges is just reduced to take account of their current state in spite of the fact that these structures continue to deteriorate. Their detailed reliability and lifetime assessment should therefore be a primary goal. Advanced methods of reliability analysis in combination with nonlinear finite element method-based analysis represent effective tools for the assessment of existing bridges. Data regarding the current level of load-bearing capacity and its expected development in the coming years (and whether or not the required level of reliability will be met) may help in the systematic scheduling of bridge maintenance and/or facilitate decision making about the effective reconstruction of the structure. This paper introduces a method for the probabilistic determination of the load-bearing capacity of bridges with respect to the progression of ongoing degradation processes over time. The method is used to determine the current load-bearing capacity of a 60-year-old reinforced concrete bridge, and for its estimation in the coming years until the end of the theoretical service life of the structure. [ABSTRACT FROM AUTHOR]

Reinforced concrete slabs, just as the other structural elements, are highly affected by the high temperatures. Due to the decrease in strength of reinforced concrete members under high temperature, bearing moment capacity of reinforced concrete slabs also decreases. In this study, a prediction model is investigated in order to determine the bearing moment capacities of reinforced concrete slabs under high temperature. Pre-calculated moment capacities of slabs exposed to fire are predicted by the implementation of adaptive neuro-fuzzy inference system (ANFIS) and the prediction performance of ANFIS model is investigated. The bending capacities of slabs with different concrete characteristics and different times of exposure are calculated. High temperature resulting from the duration of fire exposure is calculated as a function of time in accordance with ISO 834. The temperature distribution inside the slab is determined by the adoption of a steady-state one-dimensional heat transfer. The slab was separated into slim slices and the heat in each slice is determined depending on the time of exposure. Forces and resistance of materials under fire exposure are calculated by applying the reduction coefficients in Eurocode 2. Results confirm the high prediction capability of ANFIS model. [ABSTRACT FROM AUTHOR]

The application of prestress is a very effective way to prevent the cracking of the concrete slab in the negative-moment region of continuous composite girders, and using a prefabricated prestressed-concrete slab in this region is an easier option than posttensioning. To elucidate the structural response of a continuous composite box girder with a prefabricated prestressed-concrete slab, two large, 18-m-long specimens were fabricated and tested under short-term loading, and the results are reported in this paper. One, a control specimen, was a conventional composite girder with its concrete slab cast in situ, whereas the other was a composite box girder with a prefabricated prestressed-concrete slab in the negative-moment region. The relative slip between the steel girder and the concrete slab; the load-deflection response; the distribution of strain in the steel girder, reinforcement, and concrete slab; as well as the crack widths in the concrete slab were measured during the tests. The paper shows that, although the ultimate strengths of the two specimens are almost the same, the initial cracking load and serviceability limit state load of the specimen with a prefabricated prestressed-concrete slab are 3.16 and 2.61 times, respectively, those of the specimen with a conventional concrete slab. It is also shown that simple linear-elastic analysis leads to a close prediction of the load for initial cracking. By comparison, a continuous composite bridge beam with a prefabricated prestressed slab over its internal support is stiffer and less likely to experience the ingress of corrosive materials than one with a conventional RC slab is. [ABSTRACT FROM AUTHOR]

Structural members that are restrained against motion can develop internal stresses when subjected to changes in temperature. The phenomenon of temperature-induced internal stresses in superstructure members of bridges has prompted the development of codified provisions for determining superstructure temperature load effects. The objective of this study, as a means of assessing the robustness of existing design provisions for a selected bridge case, was to quantify the effect that thermal stresses have on underlying foundation systems, such as intermediate bridge piers in integral abutment bridges. The objective was met by, in part, instrumenting a multispan integral abutment bridge with temperature and bridge response remote-monitoring devices. Data obtained from the remote-monitoring program are made available in graphical form to interested parties via real-time updates on a dedicated website. Simultaneous to the field-monitoring program, a detailed analytical study of the integral abutment bridge was undertaken. Through pairing of in-service field measurements with finite-element analysis of temperature loadings on the selected bridge, the contributions to foundation stresses associated with changes in temperature in the superstructure were quantified. Findings from this study support that available design provisions are capable of leading to conservative bridge foundation designs. [ABSTRACT FROM AUTHOR]

Mit dem Einsatz von ultrahochfestem Beton und hochfester Längsbewehrung kann die Tragfähigkeit von Stahlbetonstützen deutlich erhöht werden. Um dieses Potenzial erschließen zu können, muss das Tragverhalten infolge Normalkraft und Biegung bekannt sein. Am iBMB, Fachgebiet Massivbau der TU Braunschweig, wurden im Rahmen des von der Deutschen Forschungsgemeinschaft geförderten Schwerpunktprogramms SPP 1182 [1] experimentelle und theoretische Untersuchungen zum Trag‐ und Nachbruchverhalten von Stützen aus ultrahochfestem Faserbeton (UHPFRC) mit hochfester Längsbewehrung unter zentrischem und einachsig exzentrischem Längsdruck durchgeführt. In diesem Beitrag werden die Untersuchungsergebnisse und ein hieraus abgeleiteter Vorschlag zur Bemessung von gedrungenen UHPFRC‐Stützen in Anlehnung an den EC2 [2] vorgestellt. Zugleich werden Empfehlungen zur konstruktiven Durchbildung gegeben, die ein progressives Versagen verhindern. UHPFRC‐Columns with high‐strength longitudinal reinforcement The bearing capacity of reinforced compression members can be significantly increased by the use of ultra‐high performance fibre reinforced concrete (UHPFRC) and high‐strength longitudinal reinforcement. To develop this potential for reinforced concrete columns the bearing behaviour under axial force and bending must be known. The iBMB, department of concrete structures of the TU Braunschweig, has conducted experimental and theoretical research works on the bearing and post‐fracture behaviour of UHPFRC‐columns with high‐strength longitudinal reinforcement under centric and eccentric loads within the priority program SPP 1182 [1], which was funded by the German Research Foundation. This paper presents the results of the investigations and a proposal for the dimensioning of short UHPFRC‐columns in dependence on EC2 [2] and recommendations for a structural design in order to avoid a progressive collapse. [ABSTRACT FROM AUTHOR]

Advanced numerical simulations using computers provide a robust tool for assessing the structural integrity of existing reinforced concrete (RC) structures. This paper presents an application of modern computer simulation, in the context of nonlinear finite element method (nonlinear FEM), to predict the loadbearing capacity and failure behavior of different types of RC columnslab connections strengthened by steel profiles in an existing complex industrial RC structure in Austria. Two typical connections are subjected to primary numerical investigation using nonlinear threedimensional FEM with a newly developed constitutive model for concrete. Subsequent verification tests indicate that the primary numerical analyses are quite consistent with the test observations. Postnumerical analyses of the verification tests are also carried out taking into account the measured material properties. The simulation results are in very good agreement with the test data. Based on the numerical results, the loadflow mechanisms and the load-sharing portions in the connections are identified. The ultimate loads of the rest of the connections are then determined using numerical analysis, hence no further tests are necessary. On the basis of the numerical simulations, rational decisions on the structure are made. [ABSTRACT FROM AUTHOR]

In calculation of the bearing capacity of the eccentrically loaded reinforced concrete columns, in order to consider the second order effect of bending moment in the section, the effect of bending moment enlargement coefficient is used, which includes two factors, i. e. the curvature influence coefficient of eccentricity ζ1 and the curvature influence coefficient of slenderness ratio ζ2. Some differences exist in the calculation methods of these two curvature influence coefficients among the current China design codes such as the GB 50010-2010 ' Code for design of concrete structure ' and JTG D62-2004 ' Code for design of highway reinforced concrete and prestressed concrete bridges and culverts'. Through the bearing capacity tests of 14 reinforced concrete columns, the column bearing capacities obtained from test results were compared with those calculated by code methods. The results show that the calculated bearing capacity of the specimens by the GB 50010-2010 are lower than the test ones due to the ζ2 is deleted in the code, while the calculation method of ζ1 in JTG D62-2004 is not rational since the calculated bearing capacities are larger than the test ones and tend to be unsafe for structures especially when the eccentricity is small. Based on the experimental research, parametric analyses by the finite element method were carried out, and the calculation formulas for ζ1 and ζ2 were proposed. The accuracy of the proposed calculation method was verified by the collected test results of the references. [ABSTRACT FROM AUTHOR]

The fire performance of concrete beams reinforced with GFRP rebar was studied in this paper by the method of numerical simulation and theoretical calculation. Finite element models of concrete beam heated by ISO 834 standard heating curve were developed, and the suitable thermal and thermodynamic parameters were selected for the analysis. The accuracy of FEA model was proved by the comparison with the results of fire experiments, and different influencing factors were taken into account for the parametric studies to describe the fire performance. FEA results indicate that the fire behavior of GFRP reinforced concrete beams is only controlled by three factors; loading rate, GFRP rebar position, and the time exposed in fire. Refer to the structure fire design of steel reinforceal concrete in Eurocode 2, the inhomogeneous material properties under fire exposure can be assumed as homogeneous by reduced cross-section of concrete. The load-bearing capacity of the GFRP reinforced concrete members in fire environment can be calculated by the reduction of concrete cross section exposed in fire and the equivalent strength of GFRP rebars in different positions with different temperatures. The theoretical design method proposed in this paper shows good agreement with FEA results, which can be used to calculate the bearing capacity of GFRP reinforced concrete beams in fire environment. [ABSTRACT FROM AUTHOR]

Based on tests on six L-shaped RC columns with 500 MPa steel bars, the effect of axial compression ratios and stirrup spacing on failure mode, bearing capacity, displacement, and curvature ductility of the specimens is investigated. Test results show that specimens with lower axial load and large stirrup characteristic value (larger than about 0.35) are better at ductility and seismic performance, while specimens under high axial load or with a small stirrup characteristic value (less than about 0.35) are poorer at ductility; L-shaped columns with 500 MPa steel bars show better bearing capacity and ductility in comparison with specimens with HRB400 steel bars. [ABSTRACT FROM AUTHOR]

Important buildings may be subjected to accidental loads, such as explosions or impacts, during their service life. For reinforced concrete ( RC ) frame structures, columns on the first floor are more prone to failure, compared with other components. The performances of the newly formed two-bay beams above the failed columns were determined the resistance capacity against progressive collapse of the structure. In order to investigate the mechanical characteristics and failure mechanism of the two-bay beams, tests of three 1/4-scaled RC rectangle beam-column subassemblies were carried out. It was observed that the compressive arch action was activated and the peak value of the vertical load was improved due to the compressive arch action. Based on the test results, the method to determine the vertical bearing capacity of RC two-bay beams was proposed. According to the equilibrium equations of the internal forces at the key sections of the beam, the compatibility equations of deformation, the relation between the vertical load and the deflection of the middle joint of the two-bay beam were derived. By increasing the deflection of the beam step by step, the vertical bearing capacity of the two-bay beam considering the compressive arch action can be yielded, which is taken as the maximum vertical load of the beam in the calculation. The proposed method was verified to be effective by comparing the calculated and test results. [ABSTRACT FROM AUTHOR]

Tests of reinforced concrete (RC) members under the combined loading indicated that various kinds of bearing capacity would interact each other. However, the overall interaction of various force state is not considered thoughtfully in component design, leading to potential danger of structures. Using flexure-torsion interaction to connect shear-torsion and flexure-compression interaction, a unified formula was proposed in this paper considering the overall interactions of compression, shear, flexure and torsion. Every kind of interaction bearing capacity formulae can be deduced from the unified formula and easily used to determine the security of the member under various loading states. Experimental data were compared with the calculations of the proposed formula and good agreement was obtained. Finally, reinforcement obtained by the unified formula is more reasonable and more consistent with the experimental results compared with GB 50010-2002. [ABSTRACT FROM AUTHOR]