One-way Slabs Research Articles

Time-dependent deflection of conventional, self-compacting and lightweight concrete slabs

Design codes usually define time-dependent deflection as a multiple of instantaneous deflection. Therefore, the ratio of long-term to instantaneous deflection is crucial in the design of concrete structures. The experimental results of three series of experiments on long-term deflection of conventional, lightweight and self-compacting concrete slabs under sustained loads are compared and discussed in this study. The slabs were subjected to loading at age 14 d after casting. The flexural deflection caused by two distinct levels of applied load, and the effects of the drying shrinkage and creep were monitored for 225 d for three pairs of simply supported one-way slabs. Comparative analysis of the mechanical properties of concrete types at 14 and 28 d is conducted and the creep coefficient and drying shrinkage strain in the mixtures are determined. Furthermore, individual effects of these parameters on the ratio of long-term to instantaneous deflection are discussed. The results obtained confirm that, in the existing time-dependent deflection models, the effects of loading age, load value and the environmental conditions should be included. In addition, the experimental ratio of the long-term to instantaneous deflection in slabs is far from the predictions of ACI 318-14, AS 3600-09, EN 1992.1.1 and CSA-A23-04 codes.

Relationship between the shear capacity and the flexural cracking load of FRP reinforced concrete beams

This paper focuses on the relationship between the shear capacity and the flexural cracking load of Fiber Reinforced Polymer (FRP) reinforced concrete beams without stirrups. A relationship between the cracking load that causes a beam to crack at the middle of shear span and the shear capacity of the beam is confirmed based on the test results of 29 beams. The relationship was further examined by comparing the test results of 168 FRP reinforced beams and one-way slabs that were collected from literature. All specimens were reinforced in the longitudinal direction only and tested as simply supported conditions subjected to 4-point bending. The concrete compressive strength, reinforcement ratio, shear span-to-depth ratio, and effective depth of the beams in the database were in the range of 24.1–88.3MPa, 0.12–2.63%, 1.1–6.45, and 141–1111mm, respectively. The comparison revealed that there is a strong relationship between the cracking loads and the shear capacity of the members. This relationship can be used to develop a shear design method for FRP reinforced members.

Experimental research on blast-resistance of one-way concrete slabs reinforced by BFRP bars under close-in explosion

Avoiding steel-bar-like corrosion in concrete members, basalt fiber reinforced plastic (BFRP) bars behaving as reinforcement have advantages in coastal civil engineering. One-way concrete slabs reinforced by BFRP bars (SRBBs) were designed to investigate their mechanical responses under static loads and explosions. High strength but relatively low stiffness of BFRP bars make SRBBs have different responses to slabs reinforced by steel bars (SRSBs). BFRP bars work in the elastic stage while steel bars result into plastic deformation after limited elastic deformation. SRBBs have larger deflections but higher ultimate loads compared with SRSBs in static bending tests. Explosive experiments reveal the damage patterns of SRBBs under various scaled distances, from 0.474m/kg1/3 to 0.684m/kg1/3. Crack, spall and breach are three typical damage modes for blast-loaded slabs. Compared with SRSB, the SRBB of the same reinforcement ratio and under the same scaled distance has larger deflections, but smaller damage level and greater residual loads. It is indicated that although the SRBB is not stiffer than the SRSB, it has greater anti-blast ability in current research.

Reinforced Concrete One-Way Slabs with Large Steps

Reinforced Concrete One-Way Slabs with Large Steps

Instantaneous deflection of light-weight concrete slabs

Construction loading before the age of 28 d can have the most significant effects on the slabs, especially for multi-story structures. The changing properties of the young concrete complicate the prediction of serviceability design requirements also. An experimental investigation is performed on four simply supported Light-Weight Concrete (LWC) one-way slabs subjected to immediate loading at 14 d. Effects of aggregate type, loading levels and cracking moment together with the influences of ultimate moment capacity and service moment on the instantaneous deflection of slabs are studied. Comparison of the obtained results with predictions of existing models in the literature shows considerable differences between the recorded and estimated instantaneous deflection of LWC slabs. Based on sensitivity analysis of the effective parameters, a new equation is proposed and verified to predict the instantaneous deflection of LWC slabs subjected to loading at the age of 14 d.

Flexural behavior of sustainable reactive powder concrete bubbled slab flooring elements

Voided slabs are reinforced concrete slabs in which voids allow to reduce the amount of concrete. The bubbled deck slab is a new and sustainable biaxial floor system to be used as a self-supporting concrete floor. The use of voided slabs leads to decrease the consumption of materials and improve the insulation properties for enhancing the objectives of sustainability. This study presents an investigation into the flexural behavior of sustainable Reactive Powder Concrete RPC bubbled slab flooring elements. Six one-way slabs were cast and tested up to the failure. The adopted variables in this study are: the volumetric ratio of steel fibers, type of slab; bubbled or solid, placing of reinforcement and thickness of slab. The effect of each variable on the ultimate load, deflection and strain has been discussed. The results show that increasing the percent of steel fibers from 1% to 2% in solid and bubbled slabs decreases the deflection by (18.75%) and (50%) respectively. As well as, the deflection increases by (41%) for bubbled slab compared to the solid slab. The slabs reinforced with top and bottom steel meshes show less deflection than slabs reinforced by only bottom steel mesh.

Experimental Behavior of High-Strength Concrete One-Way Slabs Subjected to Shock Loading

The design to resist blast loading is required in many private and governmental buildings. The research presented in this thesis characterizes the response of high strength concrete panels, reinforced with high strength vanadium steel, subjected to blast loading under controlled conditions. This work is intended to provide valuable data to study numerical models such as the commonly used single-degree-of-freedom (SDOF) models. The experimental procedure used and data collected from high-strength reinforced concrete (RC) slabs, having two different high-strength reinforcement ratios subjected to shockwave loadings using a blast load simulator are presented in this thesis. The pressure, impulse, and deflection time histories generated from the experiments along with the predicted panel deflection and damage responses are presented. The pressure impulse (PI) curves developed using a SDOF model are compared with the experimental data. Damage assessment generated from the blast load simulator experiments and a comparison of experimental behavior of high strength RC slabs with regular strength RC slabs, having two different Grade 60 regular-strength reinforcement ratios, are also presented. These results showed that while the regular strength slabs with regular strength reinforcing steel experienced slightly higher experimental deflections that the high strength slabs with high strength reinforcing steel, the reinforcement spacing or reinforcement ratio, played a more significant role in both experimental and numerical maximum peak deflections for both the regular strength concrete slabs reinforced with regular strength steel and the high strength concrete slabs reinforced with high strength steel. Experimental quantification of the dynamic resistance curves showed that the slabs with smaller longitudinal reinforcement spacing had greater ductility and post-yield behavior. Furthermore, a parametric study was performed, using the same SDOF model, comparing various high-strength concrete slab thicknesses with varying highstrength reinforcement ratios for maximum numerical deflection. The results from this study showed that the thicker slabs with larger reinforcement ratios yielded smaller maximum numerical deflections than those of the thinner slabs with smaller reinforcement ratios. Finally, the concrete damage patterns of the panels are shown and described.

Cohesive cracked-hinge model for simulation of fracture in one-way slabs on grade

Numerical analysis of slab on grade structures subjected to mechanical loads is a complex matter often requiring computationally expensive models. In order to develop a simplified and general concept for non-linear analysis of slab on grade structures, this paper presents a cohesive cracked-hinge model aimed at the analysis of the bending fracture of the cemented material. The model is based on the fracture mechanics concepts of the fictitious crack model with a linear stress–crack opening relationship. Moreover, the paper presents a two-parameter spring foundation model applied to realistically capture the continuity in the supporting medium. The functionality of the proposed model is compared to numerical analysis with application of the more conventional cohesive zone model. The results obtained show that the methodology is a attractive and powerful one well-suited for practical use and further development.

Precast concrete sandwich one-way slabs under flexural loading

The behavior of precast concrete sandwich panels consisting of two thin R/C layers (wythes) separated by an expanded polystyrene core is examined through experiments on prototype panels subjected to four-point bending, for different values of panel thickness and mesh size, with/without either shear-resistant ribs or conventional steel rebars (besides the wire mesh) in the bottom wythe. The test results indicate that all the panels behave as composite member until failure, and the panel behavior is similar to conventional R/C one-way slabs under flexural load. Due to the presence of wire mesh, cracking behavior in terms of number of cracks and crack spacing of concrete sandwich panels is similar to that of ferrocement cracking behavior. Volume ratio and specific surface of reinforcement affect the cracking behavior of concrete sandwich panels similar to that of ferrocement panels. The crack spacing based on predictive models for concrete slab reinforced with wire mesh agrees with the experimental results. Presence/absence of shear-resistant ribs and/or rebars in the bottom wythe significantly affects the flexural behavior of the panels. Presence of conventional rebars in the bottom wythe together with the wire mesh increases the ultimate flexural load capacity of the panels. The load-deflection response of the concrete sandwich panels exhibits trilinear behavior, and is similar to ferrocement behavior under flexural loading. Analytical study includes strength predictions based on conventional R/C beam analysis.

Modelling of bonded and unbonded post-tensioned concrete flat slabs under flexural and thermal loading

During their life span, post-tensioned concrete structures may be exposed to thermal loads. Therefore, there has been a growing interest in research on the advanced analysis and design of post-tensioned concrete slabs subjected to thermal loads. This paper investigates the structural behaviour of post-tensioned one-way spanning concrete slabs. A nonlinear finite element model for the analysis of post- tensioned unbonded and bonded concrete slabs at elevated temperatures was developed. The interface between the tendon and surrounding concrete was also modelled, allowing the tendon to retain its profile shape during the deformation of the slab. The load-deflection behaviour, load-force behaviour in the tendon, and the failure modes are presented. The numerical analysis was conducted by the finite element ANSYS software and was carried out on two different one-way concrete slabs chosen from literature. A parametric study was conducted to investigate the effect of several selected parameters on the overall behavior of post-tensioned one-way concrete slab. These parameters include the effect of tendon bonding, the effect of thermal loading and the effect of tendon profile. Comparison between uniform thermal loading and non-uniform thermal loading showed that restrained post tensioned slab with bottom surface hotter has smaller failure load capacity.

An Experimental Study on the Flexural Capacity of a One-way Void Slab with removable Deck Plate

An Experimental Study on the Flexural Capacity of a One-way Void Slab with removable Deck Plate

Flexural Strengthening of RC Slabs Using a Hybrid FRP-UHPC System Including Shear Connector

A polymeric hybrid composite system made of UHPC and CFRP was proposed as a retrofit system to enhance flexural strength and ductility of RC slabs. While the effectiveness of the proposed system was confirmed previously through testing three full-scale one-way slabs having two continuous spans, the slabs retrofitted with the hybrid system failed in shear. This sudden shear failure would stem from the excessive enhancement of the flexural strength over the shear strength. In this study, shear connectors were installed between the hybrid system and a RC slab. Using simple beam, only positive moment section was examined. Two full-scale RC slabs were cast and tested to failure: the first as a control and the second using this new strengthening technique. The proposed strengthening system increased the ultimate load carrying capacity of the slab by 70%, the stiffness by 60%, and toughness by 128%. The efficiency of shear connectors on ductile behavior of the retrofitted slab was also confirmed. After the UHPC top is separated from the slab, the shear connector transfer shear load and the slab system were in force equilibrium by compression in UHPC and tension in CFRP.

Finite element analysis and optimization of bonded post-tensioned concrete slabs

AbstractOptimization techniques may be effective in finding alternative design of post-tensioned slabs to improve their mechanical behaviour, particularly reducing the bending moments. Post-Tensioned (PT) concrete one-way slabs are one of the widely used slabs because of their good performance and cost effectiveness compared with other slab types. The objective of this study is to develop three-dimensional Finite Element (FE) model for the optimization of bonded PT concrete one-way slab. The FE software package ANSYS was used to find the optimum strain energy and area of PT tendons. The interface between PT tendon and the surrounding concretes was also modeled, allowing the tendon to keep its shape during slab deformation. Contact algorithm and material nonlinearity were considered in the FE model. The total strain energy of bonded PT concrete slab was considered as the objective function. The design variables are the area of PT tendons, the initial stress in tendons and the eccentricity of the tendon pro...

Repercussion the use phase in the life cycle assessment of structures in residential buildings using one-way slabs

This study incorporates the use phase in the life cycle assessment (LCA) of reinforced concrete structures that are composed of one-way slabs. Sustainable construction is one of the main future objectives of the European Union; therefore, useful and reliable tools will be necessary for its implementation. The usefulness of the LCA for the selection of structural alternatives depends on the data quality. The Environmental Product Declarations collect the production phase of building materials, but it is necessary to incorporate the particularities in the implementation and use phases. This work proposes a stage that considers the use phase in the structural part that does not belong to the building envelope and provides a methodology that reflects the characteristics of each climate zone where it is applied. All of the representative variables to define the structure of a building are combined: column grids, variations in the geometry of one-way slabs, and different materials. A discrete model that incorporates 360 cases is constructed to compare the reliability of the model with a study on real structure projects. The results show the importance of the use phase in residential buildings with respect to the effects generated during the other phases (production, execution and demolition), as well as its high variations, up to 140.4%.

Sensitivity analysis of Life Cycle Assessment to select reinforced concrete structures with one-way slabs

Life Cycle Assessment (LCA) tools are often applied to the production stage of structural projects. This study aims to determine the sensitivity of the real environmental impact according to aspects related to decisions made during the execution stage. This stage includes factors that are beyond the control of the planner or designer: control over production (hourly yield, waste management), location of production facilities (transport of components to building location). The present study analyzes and evaluates three variables: distance travelled for component transport, working hours, and materials wasted during the production and construction process. Limit values are established according to six possible scenarios. Based on the results, it can be concluded that hourly yield had a minimal effect on the generated environmental impact. Transport and material waste, on the other hand, are the factors that brought about the greatest variations in environmental impact. For example, the components that are most sensitive to transport can decrease environmental impact by 65.66% or increase it by 18.24% depending on project location. And when considering material wasted during production and construction, the environmental impact varied from −9.77% to 9.78%.

Experimental Investigations on the Strength and Serviceability of Biaxial Hollow Concrete Slabs

Biaxial hollow slab is a reinforced concrete slab system with a grid of internal spherical voids included to reduce the self-weight. This paper presents an experimental study of behavior of one-way prestressed concrete bubbled slabs. Twelve full-scale one-way concrete slabs of (3000mm) length with rectangular cross-sectional area of (460mm) width and (150mm) depth. Different parameters like type of specimen (solid or bubbled slabs), type of reinforcement (normal or prestress), range of PPR and diameter of plastic spheres (100 or 120mm) are considered. Due to the using of prestressing force in bubbled slabs (with ratio of plastic sphere diameter D to slab thickness H, D/H=0.67), the specimens showed an increase in ultimate load capacity ranging between (79.3% and 125%) and a decrease in the deflection at service load of about (9.8% to 12%) with respect to the control bubbled reinforced concrete slab. Also, it is found that, the bubbled slabs have about (79% to 86%) of the ultimate load capacity of a similar reference solid slab. At the same time the influence of voids present in the bubbled slabs is reflected in a decrease in the first cracking load by about (14.8% to 29.6%) in comparison with solid slabs.
 

Mechanisms of shear resistance of one-way concrete slabs reinforced with FRP bars

The shear behavior of concrete reinforced with fiber-reinforced polymer (FRP) but without web reinforcement is potentially the most critical case in shear-prone applications due to the brittle nature of the concrete and reinforcement and, as such, requires special attention. A total of 16one-way reinforced concrete slabs reinforced with glass- and carbon-FRP bars in addition to steel-reinforcement were constructed and tested to failure under four-point flexural loading. Their structural behavior was observed and reported in terms of failure mechanisms, crack patterns, main shear cracks, and ultimate capacities. The test results confirmed the effect of the axial stiffness of longitudinal FRP reinforcement on shear strength. The use of high-strength concrete had a positive impact on the initial shear-cracking load and ultimate-load capacity. The influence of the reinforcement type, bar diameter, and bar shear stiffness on the mode of failure was determined and discussed. Most of the CFRP-reinforced slabs experienced brittle failure, while most of the GFRP reinforced slabs—with reinforcement axial stiffness equivalent to that of the CFRP reinforced slabs—kept their integrity even after failure, thereby avoiding brittle modes of failure.

Flexural Behavior of Post-tensioned Lightweight Concrete Continuous One-Way Slabs

In this experimental study, six post-tensioned light weight concrete (LWC) continuous one-way slabs were tested in the following manner: the flexural behaviors of the members were compared with the calculations from the existing standards. The test also examined the effect of prestressing in tendons and proper prestress conditions to reduce the deflection and crack width, and to enhance the flexural capacity and ductility of LWC members. Flexural capacity and stress increments in unbonded tendons of the specimens were compared with those of the simply supported normal and the lightweight concrete members. The suggested safety limit from the American Concrete Institute (ACI) regulation on the maximum capacity and the stress incremental in unbonded tendons were also compared with the test results under simple and continuous supporting conditions.

Simplified full-depth precast concrete deck panel systems for accelerated bridge construction

A simplified full-depth precast concrete deck panel system for accelerating bridge construction (ABC) is introduced and a finite element analysis (FEA) is conducted to investigate the static and dynamic responses of this conceptual deck system. The FEA results are compared to those of the traditional full-depth precast concrete deck panel system. The comparison results show that the mechanical behavior of the new deck system is different from that of the traditional deck system. The concrete decks in the new system act as two-way slabs, instead of the one-way slab in the traditional system. Meanwhile, the connections in both the longitudinal and transverse directions may need to accommodate the negative moments. Compared to those in the traditional system, the longitudinal nominal stress at middle span increases a lot in the new deck system and the effective flange width varies significantly. In addition, the dynamic results show that the impact factor is influenced by the spacing of connections. Finally, some design concerns of the new deck system are proposed.

Technical and economic study of striking and clearing operations in buildings under construction. Case study in Bogotá, Colombia

El presente artículo evalúa el beneficio económico de la aplicación del Nuevo Procedimiento Simplificado (NPS), reflejado en los plazos de construcción en edificaciones de entrepisos sucesivos. El edificio de referencia corresponde a un edificio residencial resuelto con pórticos y entrepisos en una dirección, de concreto reforzado ubicado en la ciudad de Bogotá. Las fases desarrolladas en cumplimiento del objetivo planteado, constaron de una caracterización de los componentes, el estudio de distintas alternativas para determinar la transmisión de cargas entre entrepisos y puntales, y una revisión de los precios de alquiler de equipo auxiliar y personal del edificio de referencia. Aplicando dicho procedimiento se realizó una evaluación económica de los plazos obtenidos en cada una de las operaciones estudiadas. Se destaca que el análisis del proceso constructivo de la estructura de la edificación empleando el NPS permite lograr ahorros considerables en la ejecución de la edificación sin poner en riesgo la integridad de la estructura.