Hollow Reinforced Concrete Research Articles

Unified rational formula for pre-cracking torsional stiffness of solid and hollow reinforced concrete members

It is generally assumed that the elastic torsional stiffness of structural reinforced concrete (RC) members that are subjected to a torsional moment less than the cracking torque can be accurately estimated, despite a lack of adequate experimental or theoretical examination. The softened membrane model for torsion (SMMT), which has been validated experimentally, provides accurate estimates of pre-cracking torsional stiffness for solid and hollow RC members. However, the SMMT requires an iterative solution algorithm, and is thus inconvenient for design purposes. This paper presents a simplification of the SMMT and proposes a unified rational formula for the direct calculation of the initial torsional stiffness of solid and hollow RC members. The proposed formula predicts the initial torsional stiffness of nine hollow RC beam specimens almost perfectly. When used to calculate the stiffness of 147 solid and hollow RC beam specimens, the proposed formula is found to be an almost perfect simplification of the SMMT in terms of initial torsional stiffness. However, the elastic stiffness values of the 147 specimens deviate from the formula-calculated values by −40% to +50%, suggesting the values may not be as accurate as commonly presumed. It is also shown that the proposed formula can combine with an existing Tcr-θcr formula to provide a precise bi-linear simplification of the nonlinear pre-cracking torque-twist curves for solid and hollow RC members; this can then be conveniently used in the nonlinear finite element analyses needed in performance-based engineering.

Structural Behavior of Fibrous Reinforced Concrete Hollow Core One-Way Slabs Strengthening by C.F.R.P

A reinforced concrete hollow core one-way slab is one of the types of slabs used widely around the world in residential and industrial buildings to take advantage of them Economic and thermal insulation as well as to reduce the self-weight of the construction. The aim of the present study is to examine the structural behavior of the reinforced concrete hollow core one-way slabs reduce failure using the normal concrete and fibrous concrete and then strengthened using carbon fiber(CFRP)This study include molding of ( 6) specimens differ in terms of the voids volume (Vv) , volumetric percentage of steel fibers (𝑉𝑓)ا, and then strengthened by using fibers of carbon , with the aim of rehabilitation by fibers, carbon polymer (CFRP) is to find out how efficient element structural when treated after the occurrence of the failure and the validity of its use in the event of a failure has occurred entirely or partly in the roof, and re- examined using the same method and conditions that were examined ceilings is affected through it, knowing that these ceilings have been addressed and strengthened in the same way , the results of the tests of the models that have been rehabilitated using carbon fiber (CFRP), compared with the same models before strengthening and examined reduce failure, increased very high susceptibility endurance extreme , with the increase ranging from (51.6%) to (96.2%), as has been observed decrease in deflection value of models after strengthening by (CFRP).It is concluded through this study the possibility of using its concrete hollow core one-way slab as a roofing system for buildings also proved the highly efficient for this slab after rehabilitation using carbon fiber (CFRP).

Structural Behavior of Fibrous Reinforced Concrete Hollow Core One-Way Slabs Strengthening by C.F.R.P

A reinforced concrete hollow core one-way slab is one of the types of slabs used widely around the world in residential and industrial buildings to take advantage of them Economic and thermal insulation as well as to reduce the self-weight of the construction. The aim of the present study is to examine the structural behavior of the reinforced concrete hollow core one-way slabs reduce failure using the normal concrete and fibrous concrete and then strengthened using carbon fiber(CFRP)This study include molding of ( 6) specimens differ in terms of the voids volume (Vv) , volumetric percentage of steel fibers (

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It is generally assumed that the elastic torsional stiffness of structural reinforced concrete (RC) members that are subjected to a torsional moment less than the cracking torque can be accurately estimated, despite a lack of adequate experimental or theoretical examination. The softened membrane model for torsion (SMMT), which has been validated experimentally, provides accurate estimates of pre-cracking torsional stiffness for solid and hollow RC members. However, the SMMT requires an iterative solution algorithm, and is thus inconvenient for design purposes. This paper presents a simplification of the SMMT and proposes a unified rational formula for the direct calculation of the initial torsional stiffness of solid and hollow RC members. The proposed formula predicts the initial torsional stiffness of nine hollow RC beam specimens almost perfectly. When used to calculate the stiffness of 147 solid and hollow RC beam specimens, the proposed formula is found to be an almost perfect simplification of the SMMT in terms of initial torsional stiffness. However, the elastic stiffness values of the 147 specimens deviate from the formula-calculated values by −40% to +50%, suggesting the values may not be as accurate as commonly presumed. It is also shown that the proposed formula can combine with an existing Tcr-θcr formula to provide a precise bi-linear simplification of the nonlinear pre-cracking torque-twist curves for solid and hollow RC members; this can then be conveniently used in the nonlinear finite element analyses needed in performance-based engineering.

Constitutive relationships of concrete for hollow RC members in pure torsion

The softened truss model (STM) has been used to analyse the torsional behaviour of concrete members since the 1980s. However, methods based on the STM neglect the effect of concrete tensile stress and hence can only predict the post-cracking responses. A recent rational torsion model, the softened membrane model for torsion (SMMT), successfully incorporates the effect of concrete tensile stress and can predict the entire torque–twist curve, including the pre- and post-cracking branches. However, the SMMT is limited to solid-sectioned reinforced concrete (RC) members and there are still no rational torsion theories available for predicting the entire torque–twist responses of hollow RC members. In this study, the SMMT is modified to circumscribe the shear flow zone in the wall thickness of a hollow cross-section. Based on 38 hollow RC beam specimens from previously reported experiments, the amplification factor for the pre-cracking stiffness and the peak-stress strain of the tensile stress–stress relationship of concrete is quantified to be 1·15, and a multiplier factor for the average tensile and compressive stresses of concrete is proposed for hollow RC members. The new constitutive relationships of concrete and the modified SMMT closely predict the cracking torques of the 38 hollow specimens and estimate the entire torque–twist curves of 27 eligible specimens very well; they are also validated using four large specimens from a recent experiment conducted as part of this study. A detailed comparison and discussion of the analyses and experiments is presented.

Thermal Isolation Character of Reinforced Concrete Hollow Floor

Reinforced Concrete Hollow floor system was named by its typical inner core and worked as an excellent horizontal bearing structure. It has fine mechanical ability and good thermal isolation character. The author compared reinforced concrete hollow floors and traditional reinforced concrete floor. And studied their development in long span or large loaded building.

Performance assessment of hollow RC bridge columns with triangular reinforcement details

The aim of this study was to assess the performance of hollow reinforced concrete (RC) bridge columns with triangular reinforcement details for materials quantity reduction and to provide data for developing improved design criteria. Hollow column sections are designed based on the economic considerations of the cost savings associated with reduced materials and design moments compared with increased construction complexity and hence increased labour costs. The proposed triangular reinforcement details are economically feasible and rational and facilitate shorter construction periods. Five hollow RC bridge columns were tested under a constant axial load and a cyclically reversed horizontal load. The effect of the proposed reinforcement details on the performance of hollow bridge columns was investigated. The computer program RCAHEST (Reinforced concrete analysis in higher evaluation system technology) was used to analyse RC structures. The proposed numerical method for the performance assessment of hollow RC bridge columns was verified by comparison with experimental results. As a result, the proposed reinforcement details were designed prior to the existing reinforcement details in terms of required performance. Additionally, the studies and discussions presented here provide insight into the key behavioural aspects of hollow RC bridge columns with triangular reinforcement details.

Performance assessment of hollow RC bridge column sections with reinforcement details for material quantity reduction

The purpose of this study was to investigate the performance of hollow reinforced concrete (RC) bridge column sections with reinforcement details for material quantity reduction. Hollow column sections are based on economic considerations of the cost savings associated with reduced material and design moments compared with increased construction complexity and hence increased labour costs. The proposed reinforcement details demonstrate economic feasibility and rationality, and facilitate shorter construction periods. Models of hollow column sections with reinforcement details for material quantity reduction were tested under quasi-static monotonic loading. The proposed reinforcement details for material quantity reduction were equal to the existing reinforcement details in terms of required performance. The computer program RCAHEST (Reinforced concrete analysis in higher evaluation system technology) was used for the analysis of RC structures. A modified lateral confining effect model was adopted for hollow bridge column sections. This study documents the testing of hollow RC bridge column sections with reinforcement details for material quantity reduction and presents conclusions based on the experimental and analytical findings. Additional full-scale experimental research is needed to refine and confirm design details, especially for the actual detailing employed in the field.

Experimental study of hollow rectangular bridge column performance under vertical and cyclically bilateral loads

To investigate the seismic performance of hollow reinforced concrete (RC) bridge columns of rectangular cross section under constant axial load and cyclically biaxial bending, five specimens were tested. A parametric study is carried out for different axial load ratios, longitudinal reinforcement ratios and lateral reinforcement ratios. The experimental results showed that all tested specimens failed in the flexural failure mode and their ultimate performance was dominated by flexural capacity, which is represented by the rupture/buckling of tensile longitudinal rebars at the bottom of the bridge columns. Biaxial force and displacement hysteresis loops showed significant stiffness and strength degradations, and the pinching effect and coupling interaction effect of both directions severely decrease the structural seismic resistance. However, the measured ductility coefficient varying from 3.5 to 5.7 and the equivalent viscous damping ratio varying from 0.19 and 0.26 can meet the requirements of the seismic design. The hollow RC rectangular bridge columns with configurations of lateral reinforcement in this study have excellent performance under bidirectional earthquake excitations, and may be considered as a substitute for current hollow RC rectangular section configurations described in the Guideline for Seismic Design of Highway Bridges (JTG/T B02-01-2008). The length of the plastic hinge region was found to approach one sixth of the hollow RC rectangular bridge column height for all specimen columns, and it was much less than those specified in the current JTG/T. Thus, the length of the plastic hinge region is more concentrated for RC rectangular hollow bridge columns.

Fatigue Test Studies on Reinforced Concrete Hollow Slab Girder

Reinforced Concrete (RC) Hollow Slab Girder is widely used in Highway Engineering, and fatigue load is an essential aspect of causing damage. In order to accurately calculate the distribution and development laws of RC hollow slab girder fatigue strain, experiment on Amplitude fatigue with five experimental beams were done in the laboratory. The beams obviously presented a rule of three stages: the damage development is fast in fore period and later period; but the hazard from fatigue in the midterm developed steadily relatively. The destruction of fatigue damage is the steel brittle fracture. Fatigue failure could be divided into three periods: rapid development stage, stable stage and destruction stage. In last stage one or two main cracks continues to expand, the rest stop growing and gradually closed, it fatigue fractured at the main crack. With the increase of the number of cycles of fatigue loading, the growth rate slowed down into a relatively stable stage, when approaching destruction there is relatively substantially growth.

Shear strength model for reinforced concrete rectangular hollow columns

The primary purpose of this paper is to propose an assessment model for concrete contribution to the shear strength of reinforced concrete (RC) rectangular hollow columns subjected to lateral loading. The model was developed based on the test results of this study, as well as other hollow column tests available in literature. A total of thirteen ¼-scale RC rectangular hollow columns, with no transverse reinforcement, were tested under lateral loading in this study. The test variables included column length-to-depth aspect ratio, longitudinal steel ratio, hollow section ratio, web-to-gross section area ratio, and loading pattern. Also, a database of almost all RC hollow column tests available worldwide was assembled and used in quantifying the effect of increasing ductility on the column shear strength. Several popular shear models proposed earlier, all of which were mainly based on tests for columns with solid sections, were reviewed and compared with the developed model.

Interaction of Curves Proposed for Design and Analysis of Hollow Reinforced Concrete Columns

Interaction of Curves Proposed for Design and Analysis of Hollow Reinforced Concrete Columns

The Method of Sandwich Plate about Thin-Wall Cast-in-Site Reinforced Concrete Hollow Floor

Treat the upper plate and lower plate of ribbed hollow floor as the surfaces of sandwich panel, and the ribbed hollow layer as the central layer of sandwich panel; consider the bending stiffness of the surfaces and transverse shear deformation of the central layer; use Hoff laminated theory; based on the same stiffness principle; establish sandwich panel structure model of hollow floor; Derive partial differential equations of cast-in-place reinforced concrete two-way ribbed and thin-walled hollow floor under vertical uniform load and present the analytic solution of the equations with two opposite clamped edges and others simply supported edges. Analyze the mechanical properties of hollow floor. The results are very close to the results of using finite element method.

Design Formulas for Cracking Torque and Twist in Hollow Reinforced Concrete Members

Hollow concrete members are in wide use and are becoming increasingly important in terms of energy savings and carbon reduction. To date, the prediction of cracking torque in hollow reinforced concrete (RC) members still relies on simplistic empirical formulas, and the accuracy of the existing formulas is rarely examined. In this study, four existing formulas are used to calculate the cracking torques Tcr and twists qcr of 44 hollow RC beam specimens currently available in the literature. An existing empirical formula for Tcr is modified to fit the test values. Based on the latest rational formula for solid members, a new formula for the Tcr and qcr of hollow RC members is developed to form a unified formula for solid and hollow sections. The predicting accuracies of these formulas are compared and evaluated. It is shown that the proposed formulas produce significantly more accurate and reliable predictions than the existing formulas.

Seismic Performance Assessment of Hollow Reinforced Concrete and Prestressed Concrete Bridge Columns

The aim of this study is to assess the seismic performance of hollow reinforced concrete and prestressed concrete bridge columns, and to provide data for developing improved seismic design criteria. By using a sophisticated nonlinear finite element analysis program, the accuracy and objectivity of the assessment process can be enhanced. A computer program, RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), is used to analyze reinforced concrete and prestressed concrete structures. Tensile, compressive and shear models of cracked concrete and models of reinforcing and prestressing steel were used to account for the material nonlinearity of reinforced concrete and prestressed concrete. The smeared crack approach was incorporated. The proposed numerical method for the seismic performance assessment of hollow reinforced concrete and prestressed concrete bridge columns is verified by comparing it with the reliable experimental results. Additionally, the studies and discussions presented in this investigation provide an insight into the key behavioral aspects of hollow reinforced concrete and prestressed concrete bridge columns.

Concrete contribution to initial shear strength of RC hollow bridge columns

The primary objective of this study was to identify concrete contribution to the initial shear strength of reinforced concrete (RC) hollow columns under lateral loading. Seven large-scale RC rectangular hollow column specimens were tested under monotonic or cyclic lateral loads. The most important design parameter was column length-to-depth aspect ratio ranging between 1.5 and 3.0, and the other test variables included web area ratio, hollow section ratio, and loading history. The tests showed that the initial shear strength reduced in a linear pattern as the column aspect ratio increased, and one specimen tested under cyclic loading achieved approximately 83% of the shear strength of the companion specimen under monotonic loading. Also, several pioneering shear models proposed around the world, all of which were mainly based on tests for columns with solid sections, were reviewed and compared with the test results of this study, for their possible applications to columns with hollow sections. After all, an empirical equation was proposed for concrete contribution to the initial shear strength of RC hollow columns based on fundamental mechanics and the test results.

Retrofit of RC hollow piers with CFRP sheets

Hollow bridge piers, particularly those built before the seventies, often have insufficient shear capacity due to inadequate transverse reinforcement details. Therefore, special attention must be given to this very important aspect when reinforced concrete (RC) piers with hollow sections are analysed and retrofitted. This paper covers the experimental analysis of retrofit solutions using CFRP sheets along the piers’ entire height to prevent shear failure. Experimental cyclic tests were carried out to evaluate the shear retrofit strategy efficiency on a set of RC piers with square hollow sections. This work also covers the study of design procedures for CFRP shear retrofitting and the evaluation of the associated ductility capacity improvement. The various transverse reinforcement detailing scenarios were assessed to determine their shear-failure prevention efficiency. The corresponding cyclic response behavior was also evaluated. The most relevant experimental information is presented in the paper, such as the evolution of the outer damage pattern. Finally, shear retrofit solutions, with a 40% increase over the maximum flexural force, show that this strategy is adequate to allow satisfactory ductility behavior.

Shear-Lag Phenomenon in Cast-in-Site Reinforced Concrete Hollow Floor System

Shear-lag phenomenon exits in many long-web structure especially when the stiffness of web is much larger than that of the flange’s. In this paper, Energy-Variation Method is applied to interpret shear-lag phenomenon in cast-in-site reinforced concrete hollow floor system. Finite Element Method (FEM) and is then used to validate the analysis results. The solution for the variation equation for effective flange width is proposed by solving the differential equations using proper boundary conditions.

Study on Mechanical Behaviors of New Reinforced Concrete Hollow Floor Slab

In this paper a new type of reinforced concrete four-way rib hollow slab was proposed by the authors first. Further in order to research on the mechanical properties of the new floor slab the other two common slabs were compared with the new one, that was two-way rib hollow slab and solid slab. The rational finite element (FE) models of the three kinds of slabs supported by four corner columns were built up respectively by ANSYS. The deflection and stress of the three kinds of slabs under three load cases were calculated separately, on the basis of which thorough comparisons and analysis were carried out. The study results showed that the new reinforced concrete four-way rib hollow floor slab has superior mechanical properties.

Analysis of RC Hollow Columns Strengthened with GFRP

Reinforced concrete (RC) hollow piers in bridges withstand high moment and shear demands ensured with reduced mass and lower stress on foundations compared with solid piers. Failure of hollow columns is typically affected by premature buckling of reinforcing bars and concrete cover spalling. At present, no guidelines are available for the design of their upgrade, and few research investigations can be found on hollow columns strengthened by using fiber-reinforced polymer (FRP) materials. This paper discusses an experimental program carried out on purely compressed RC hollow columns externally wrapped with glass-fiber-reinforced polymer (GFRP). Three specimens were tested: one specimen was unstrengthened and used as the benchmark; the other two specimens were GFRP-wrapped with different confining reinforcement ratios. Each specimen was designed according to dated codes (i.e., prior to 1970) accounting only for gravity loads. In particular, steel longitudinal bars cross section and steel tie-spacing were designed with the minimum amount of longitudinal reinforcement and minimum tie area at maximum spacing. Tests results highlight that the GFRP-jacket mainly provided ductility increases before low strength increments could be obtained. Refined and simplified numerical models for hollow square RC columns, previously proposed by the authors, herein extend to hollow rectangular members. Comparisons of experimental results and theoretical predictions on the basis of both refined and simplified confinement models were performed and showed good agreement. In the case of the simplified model, a value for the effective ultimate FRP strain was suggested.