Slab Elements Research Articles

Robustness of Dry‐Assembled Precast Wall and Coupled Wall‐Frame High‐Rise Structures With Voided Prestressed Slabs

ABSTRACTPrecast concrete structures are recognized among the structural typologies that may mostly suffer from progressive collapse as a consequence of local unpredicted damage, also due to past accidents occurred in buildings employing old precast technologies neglecting the basic robustness criteria and characterized by poorly detailed and/or executed joints and connections. Although vertical ties may relatively easily be provided in both frame and wall panel structures by employing ductile connection devices, dry‐assembled precast systems avoiding concrete pouring in the whole superstructure typically struggle to provide horizontal ties as strong as required by the current standards concerning progressive collapse, in which they are not fully framed yet. Nevertheless, these systems may exploit alternative sources of robustness to stop collapse progression arising from their structural arrangement, the shape of the slab elements employed, and the slab mechanical connections. This article presents the results of a numerical investigation focused on the structural behavior of a dry‐assembled precast floor system consisting of prestressed box‐section slab elements employed in either wall panel or coupled wall‐frame structural systems following the loss of one or multiple primary load‐bearing vertical elements. Nonlinear static simulations of different loss scenarios occurring in prototypes of 100‐m‐tall high‐rise buildings were carried out based upon spread plasticity modeling of the structural elements and experimentally calibrated nonlinear behavior of mechanical connections.

Analysis of the Effect of Layer Height on the Interlayer Bond in Self-Compacting Concrete Mix in Slab Elements.

This paper presents a study on the influence of the layered casting technology of self-compacting concrete (SCC) on the load-bearing capacity of interlayer bond in slab elements. The research was conducted on slab elements with dimensions of 750 × 750 × 150 mm, concreted from a single point of concrete delivery. The aim of this study was to analyse the influence of the height of the concreting top layer on the bond strength between the layers. The study utilised top layer heights of 50, 75, and 100 mm, which, according to the authors' experience, are the most common cases when making slab elements. The interlayer bond was determined by investigating the splitting tensile strength of cubic specimens cut from the concrete slabs. Computed tomography (CT) was employed to image the contact zone between the concrete layers. Based on the analysis of the CT imaging and the results of the strength tests, it was shown that the interlayer bond is influenced by both the height of the top layer and its free-spread distance from the casting point. A reduction in the interlayer bond strength was observed with decreasing the height of the top layer and increasing distance from the mixture supply point. The relationships obtained were linear and had a clearly negative slope. It was concluded that the valid recommendations and standards for the multilayer casting of SCC are too general. Therefore, we propose to detail the recommendations to reduce the risk of cold joints, which diminish the bond strength of the interlayer joints.

PERFORMANCE OF BAMBOO- AND GLASS-FIBRE-REINFORCED CONCRETE SLAB SUBJECTED TO STATIC AND CYCLIC LOADS

In the construction field, mild steel is using as reinforcement in concrete, which can easily corrode and destroy the environment. So, the construction industries are focusing on alternate materials like natural and synthetic fibres for sustainability. In this study bamboo, glass-fibre bars were used as reinforcement and compared with a normal reinforced concrete slab subject to static and cyclic incremental loading conditions. According to this, the experimental studies were carried out on 9 slab elements of size 600 mm × 450 mm with different forms of reinforcement. The slab elements’ deflection, deformation, load-carrying capacity, stress, strain, crack patterns, stiffness and energy absorption were determined and compared. The ultimate load-carrying capacity of elements like conventional, GFRP and bamboo are 28.90 kN, 29.31 kN and 5.50 kN respectively; similarly, deflection 12.70 mm, 13.50 mm and 8.60 mm were found under static load. In the same way, the ultimate load-carrying capacities of the elements are 24.23 kN, 25.00 kN and 6.80 kN under cyclic loading conditions; deflections of 10.10 mm, 13.50 mm and 3.60 mm, respectively, on conventional, GFRP and bamboo elements. From the test results the stress, strain, energy absorptions were calculated and compared and the energy absorption of bamboo was 9.38% less than conventional and GFRP was 22.49 % higher than conventional elements. The study proved that GFRP material has a significant impact than conventional and bamboo elements and the bamboo reinforcement can be used in light-loading conditions.

THE FLEXURAL BEHAVIOR OF SUSTAINABLE LIGHTWEIGHT CONCRETE HOLLOW CORE SLABS

Hollow slabs are reinforced concrete slabs with voids that enable less concrete to be used. To promote sustainability goals, this type of slab reduces material use and enhances insulating characteristics. This paper presents an experimental program for studying the flexural behavior of the sustainable hollow Slab elements of lightweight concrete with three different ratios of mixes using additives to choose the best ratio, which is then compared to a solid model with the same concrete mix with the best characteristics to clarify the variations in the structural behavior of voided slabs. In this investigation, hollow slabs with circular plastic tubes of 50mm diameter and 1020 mm length were used, organized as continuous voids with 30 mm spacing between the tubes. Three slabs were created, each measuring 1020 mm long, 420 mm wide, and 100 mm thick. All three slabs were tested via four-point loading. The best mix ratio was chosen and used to build a robust model. To analyse the key advantages of this technology over typical solid slabs, this solid model was compared to the best-performing model among the three hollow core slabs. Several properties such as load-carrying capability, deflection, crack patterns, and failure modes were observed in all loading steps. The results showed that using uniformly distributed uniaxial voids in the slab reduced concrete use by 23% as compared to solid slabs, Notably, the specimen with 200 kg/m3 lightweight aggregate demonstrated greater crack distribution and crack breadth.

A concrete answer for circular construction: three prototypes reusing saw-cut elements

Existing concrete buildings should be retained for as long as possible to reduce the environmental burden of demolition and new construction. However, when urban pressure makes demolition unavoidable, salvaging and reusing concrete elements elsewhere in new structures, rather than reducing them to rubble, efficiently prolongs the use of existing resources at their highest structural value. Concrete reuse is not a new approach: pioneer cases have demonstrated its potential, but broader adoption has still not been seen across the wider industry. Three prototypes recently built by Ecole Polytechnique Fédérale de Lausanne researchers and students in Switzerland demonstrate the feasibility and potential of reusing elements saw-cut from cast in situ concrete structures. The prototypes deal with different scales of elements, from small blocks to large slab elements and 3D assemblies. Lifecycle assessments confirm that reusing concrete elements drastically reduces the upfront global warming potential of new construction, providing a new lower-bound benchmark for sustainable, circular construction.

Parametric design of 3D printed ribbed slab system based on nature-inspired patterns

The interest in pattern geometry and its application to architecture may be seen throughout history. While some authors were fascinated by pattern aesthetics, others were focused on their effectiveness and underlying principles of pattern formation. In continuing with the work of the second group of authors, this paper reviews opportunities for efficient ways of implementing patterns in the design of architectural elements, supported by recent developments in parametric design and digital fabrication techniques. This paper aims to analyze pattern configurations found in nature in order to determine the underlying generation principles and the potential of their application for 3D printed slab systems. Using case study methodology, selected patterns will be applied in developing a generative parametric design system, which will further be tested in creating and (small-scale) fabricating ribbed slab elements. The result of the research is the generalization of a design approach based on principles of natural pattern formation to produce sustainable design solutions that rely on the transposition of the inherent efficiency of natural systems, such as low energy or material consumption.

Investigation on the influence of fiber fraction and orientation on the mechanical properties of fiber‐reinforced concrete slabs

AbstractThe current work examines an experimental and numerical investigation into how steel fiber reinforced concrete (SFRC) slab failure behavior is influenced by fiber orientation by pouring concrete in slab elements. Double‐ended hooked steel fibers with an aspect ratio of 50 were used in varying percentages by volume. Fresh and hardened properties of SFRC were determined based on slump flow, V‐funnel, L‐box, J‐ring test, compression, and flexure tests. The effects of different pouring/casting locations (center and corner), fiber orientation, and fiber content (0, 0.5%, and 1.0%) on the crack pattern of the SFRC slab were observed. While casting, the concrete was allowed to flow through a 30° chute angle to enhance the flowability of concrete. The SFRC slabs without fiber reinforcement undergo brittle failure without forming any prior micro cracks. Slabs with fibers experience ductile failure and show significant post‐cracking strength. The concrete's pouring position only affects the failure crack's inclination for the given workability. In the case of the corner cast slab, the crack was propagated from one edge to the opposite edge of the slab in a straight line and split into two halves. This crack pattern suggested that the fiber distribution was concentrated in half of the slab part in which the pouring corner was located. Adding 0.5% and 1.0% fiber content increased the load‐carrying capacity of slabs by 1.31 and 2.15 times, respectively. In addition to fiber content, the pouring position of concrete also made a difference in the load‐carrying capacity of slabs. The concrete pouring in the slab from the center position with 0.5% and 1.0% fiber content has 17.2% and 40% more load‐carrying capacity compared to the concrete poured in the slab from the corner position with the same fiber content. The deflection and load‐carrying capacity obtained through finite element modeling (FEM) fit the experimental results well.

Impact Energy Absorption of Sisal Fiber Reinforced Ferrocement Slab Elements and Its Statistical Relationship with Composite Compressive Strength

This study evaluates the level of energy absorption of sisal fiber reinforced ferrocement (SFRFC) slab elements of size 300 mm × 300 mm × 25 mm) (thickness) through low-velocity impact tests. The slabs are reinforced with 2 and 3 layers of steel weld mesh as primary reinforcement; and the sisal fibers of short and long fiber length, S-FL = 20 mm and L-FL = 40 mm (respectively) of varying volume fraction, (FVf of = 0.25–1.00%) act as secondary reinforcement. The compressive, split-tensile strength and flexural strength of hardened sisal fibrous mortar and plain (control) mortar specimens are determined and presented. The initial impact energy absorption (IIEA) and ultimate impact energy absorption (UIEA) of SFRFC slabs were found to be higher than ferrocement (FC-control) slabs (reinforced with 2 and 3 layers of steel mesh) demonstrating the effective contribution of sisal fibers in improving the performance of ferrocement slabs. When the length of the sisal fibers was increased from 20 mm to 40 mm in SFRFC slab elements (in hybrid combinations of steel mesh of 2–3 layers and fiber volume fraction of 0.25–1%), the impact resistance has increased several-fold over FC-control slabs. The composite compressive strength (CCS) of SFRFC has substantially increased when sisal fibers (of short and long fibers) of fiber volume fraction (FVf = 0.25–1%) are added to FC-control slab elements. Statistical prediction models have been developed separately for three dependent variables, IIEA, UIEA and CCS keeping constant the four independent variables, mesh layers (ML), fiber volume fraction (FVf), fiber length (FL) and mortar compressive strength (MCS), and the predicted values matched with the experimental results, within the acceptable error range. This study has statistically established a significant relationship between UIEA and CCS of sisal fiber reinforced ferrocement (SFRFC) slab elements.

Bending resistance of steel‐timber composite (STC) beams: analytical vs. numerical investigations

AbstractThis contribution presents the results of analytical and numerical investigations of the ultimate bending resistance of simply supported steel‐timber composite beams with uniformly distributed load, they consist of three main components: (i) the laminated veneer lumber (LVL) slab, (ii) the downstand steel beam (IPE‐profile) connected by means of (iii) demountable shear connectors, which allow for deconstruction and circular reuse of the steel beam as well as the timber slab element. The mechanical properties of the cross‐banded LVL as well as the load‐slip curves of demountable shear connectors, which have been obtained experimentally, were implemented in both the analytical and numerical models. In this paper both solutions have been compared, first the ultimate bending resistance was calculated analytically through a strain‐controlled approach with various degrees of shear connection. Then, numerical simulations were conducted in the finite element software ABAQUS to determine the ultimate bending capacity and the load‐deformation behaviour. Finally, the results of both approaches are presented and compared.

R.C.C Shell Structure Design of Selected Head Cap Shape

Abstract: A shell structure is a thin structure composed of curved sheets of material, so that Shell structures are inspired from natural element named “SHELL”. A thin curved member or slab usually of reinforced concrete that function as tension member and shell. The waviness plays an important role in the structural behavior realizing a spatial form. Some of natural elements like eggshell, seashell, fruit shells (walnut) etc are showing shell structure properties. The present reinforced concrete shells as a very efficient structure, spanning wide, architectonically beautiful, relevant and valuable structural solution. Shell structures are very attractive lightweight structures, which are especially suited to Architectural building, industrial application, commercial projects etc.. The actual design of shells, involves theories of shells and the use of appropriate codes of practice. Types of curved shell like Parabolic, Hyperbolic or Cylindrical members are often said to act as tension rigidity hence called tensile members. For achieving the optimized load capability and flexural strength of such an element in form of shell covering structure is checked in for M30 grade concrete. Tensile shell members are structural edifice that caries only tension and without buckling or bending. Tensile structures are the most common type of thin-shell structures used worldwide from past decades. The profile and aspect of structure used are unlike for loading conditions, geographical locations and Architecture design differs as such as horizontal, sloping or curved member (dome and shell member). In this research work the tensile shell (plate) structure is designed in the form of beam and as grid shell slab element (plate). After then load has been applied for analysis via software tool i.e. STAAD Pro. The types of load assigned dead and live loads. The Design code specifications for curved shell member in IS: 2210–1994, IS 2204-1962 “Code of practice for construction of reinforced concrete shell roof” [CED 13: Building Construction Practices including Painting, Varnishing and Allied Finishing] and the load case criteria is to be as per IS: 875(2)–2000. RCC design specifications as per IS: 456–2000

Deck Slab Elements for the Accelerated Construction of Steel–Concrete Composite Bridges

Various methods have been developed to produce deck slabs for steel–concrete composite bridges. Usually, the deck slabs are cast with in situ concrete using a formwork carriage, resulting in construction progress of 15 to 25 m of deck slab per week. A new construction method was developed at the Institute of Structural Engineering (TU Wien), which enables the swift erection of the concrete deck slab. This method employs precast deck slab elements with reinforced concrete cross-beams which span in the transverse direction. With this new construction method, producing up to two deck slab sections of 15–25 m per day becomes possible. Further, the performance of novel reinforcement detailing required for the precast deck slab elements is investigated by structural testing. The experiments consist of eight load-bearing tests on four specimens which represent sections of the element during casting and after completion. The investigated parameters in series 1 are the length and spacing of loops, used for protruding longitudinal bars enclosure. In series 2, the enclosure of the shear reinforcement and the height of the cross beams are varied. The results show that the targeted bending capacity could be reached in all tests with no signs of premature failure due to detailing reasons. Based on the experimental results, the feasibility of the new approach is shown and recommendations for detailing are given.

Simple Slab Elements for Environmentally Friendly Construction Technology

Concrete industry poses a great threat to the environment not only by its consumption of natural resources, but also in its role on the global emission of carbon dioxide in the atmosphere from cement industries which in turn results into global warming. In light of these scenarios, serious interventions have to be incorporated in designs to promote sustainable construction and prevent environmental pollution and degradation. In order to minimize the use of cement, a study has been done by developing simple soil arch elements which can be used to support the topping concrete slab of around 30 mm thick. The technique utilizes the semi-prefab technology and therefore eliminates the use of shuttering for slab panel construction. Through this study, it has been shown that the consumption of cement is reduced to 49.32% while the timber formwork is reduced to 60.00%. The technique is recommended for application in upper floor slab casting as it reduces the cost of construction and is environmentally friendly.

Demountable reinforced concrete slabs using dry connections

The results of an experimental investigation of a new dry connection for reinforced concrete slab elements are presented. Seven full-scale slabs were tested; one slab was monolithic and used as a control specimen, while the other six were assembled using top and bottom steel plates joined by steel bolts with high tensile strength. Two connection scenarios were investigated – a simple bolted connection and a connection with a shear key. The parameters studied were the use of stirrups at the connection section, the step size of the shear key, the bolt diameter and the number of bolts. The test results showed that using a shear key at the assembled section in demountable slabs was more efficient than the simple bolted connection, providing higher flexural stiffness, greater load capacity and less deflection. However, increasing the shear key step size improved the flexural performance of the demountable slabs. In addition, adding stirrups in the assembled section enhanced the flexural stiffness and the total load capacity of the demountable slabs. Predictions of the moment capacity and deflection of the demountable slabs showed reasonably good agreement with the experimental results but, to be generalised, additional calibrated data from experiments are required.

Cracking Behavior and High-Temperature Thermoplastic Analysis of 09CrCuSb Steel Billets

This paper characterizes the surface crack morphology and elements of 09CrCuSb steel continuous casting slabs and studies the high-temperature thermo-plasticity of continuous casting slabs using a Gleeble 3500 thermal simulator. Combining the macro/micro fracture morphology and microstructure characteristics, the formation rules of slab cracks are discussed. The research results show that the increase in Ae3 temperature caused by changes in alloy elements results in the precipitation of a thin, film-like coexisting ferrite along the grain boundaries at a certain temperature, as well as the element segregation behavior of low-melting-point alloy elements at the original austenite grain boundaries, which are the main factors inducing cracks in 09CrCuSb steel continuous casting billets. The plasticity of 09CrCuSb steel at high temperatures is poor at 800~900 °C. In continuous casting process control, it is necessary to try to avoid long-term stay of the billet at this temperature range.

The flexural behavior of Hollow core concrete slabs with different shape

Hollow slabs are slabs of reinforced concrete in which voids allow the concrete to be reduced in size. This type of slab results in reduced raw materials Consumption and increased insulating properties to achieve sustainability goals. This paper reported an experimental research program focused on the study of the bending behaviour of the elements of hollow slabs of normal-strength concrete. Three models of the one-way concrete slab were cast, It had dimensions of 1020 mm length, 420 mm width, and 100 mm thickness. The first model did not contain holes (solid) and the second model contained five circler opening holes with a 50 mm diameter, while the third model contained five square opening holes with 44 mm dimension, where the area of the second and third model were the same despite the difference in the shape of the opening. The results showed that the bearing capacity of the circular hollow core slab is higher by 12% compared to the square hollow core slab according to the type of voids and both of holes made the hollow core slab with a decrease in load capacity of 11% to 25% when compared to the solid slab. The solid slab has lower deflection value compared to the two hollow slabs whose weight is reduced by 23% compared to the solid slab.

Effect of multilayer casting technology of self-compacting concrete slabs on the load-bearing capacity of a layer-to-layer joint

The article summarizes research on the impact of the technology of casting multiple concrete layers on the load-carrying capacity of a layer-to-layer joint in the case of self-compacting concrete. The studies involved slab elements having dimensions of 1200 × 600 × 150 mm concreted from a single casting point. Two technological variants of practical realization of a joint between SCC layers were analysed: no interference in the first layer and mechanical interference into the first layer. Three delay times – 15, 30 and 60 min – were introduced between successive layers. The load capacity of the joint was found through tests of tensile strength by splitting cubic samples cut out of the slabs. X-ray computed tomography (CT) was employed to obtain images of the concrete layer contact zone. On the basis of the outcome of the strength tests and the analysis of the contact zone between the layers, it is concluded that there are three factors determining the reduction of the load-bearing capacity of the joint: delay between successive layers, distance to the casting point, first layer preparation technology. The present-day recommendations and standard guidelines concerning multilayer casting using self-compacting concrete seem to be insufficiently detailed. New recommendations are proposed aiming to limit the risk of cold joint formation and thereby the decrease of the load-bearing capacity of a joint.

Tests of demountable reinforced concrete slabs

This paper presents an experimental investigation of demountable reinforced concrete slabs using dry connections between reinforced concrete slab elements. The test specimens comprised six full-scale reinforced concrete slabs; one control slab monolithically cast, while the other five slabs were produced with mid-span demountable dry connections. The slab elements were cast separately and assembled using top and bottom steel plates joined to each side of the slab element by high tensile steel bolts with or without a shear key and embedded steel block. Theoretical analysis of the behaviour of the demountable slabs tested in comparison with the control specimen was also conducted.The test results showed that using a dry connection consisting of a shear key at the assembled section is the most effective technique in terms of moment resistance, deflection, and flexural stiffness. On the other hand, the dry connection with embedded steel blocks failed prematurely because of stress concentration at the block edges. The moment capacity and deflection predictions of demountable slabs have reasonably correlated with the experimental results but required additional calibrated data from experiments.

Experimental performance of novel cost – effective hybrid composite slabs made with cementitious composite

The present research investigation introduced a new design system for making cementitious structural elements. This study emphasizes on novel hybrid composite slab elements. The combination of newly formed hybrid fiber reinforced engineered cementitious composite (HECC) and self-consolidation concrete (SCC) was used to make slabs. The main objective of this study was to introduce novel kind of cost effective and greener HECC structural elements. In this study total 13 types of slabs were casted based on the 7 different cement mixes. To analyse the behaviour of slab specimens cracking loads, load-deflection behaviour, energy absorption capacity, flexural strength capacity, general failure pattern, ecological and economical aspects was recorded. The results from current experimental approach depicted that new composite slab system enhanced the flexural performance, energy absorption, service life and ductility of slab specimens. Construction of slabs with HC approach reduced the global warming potential (GWP), embodied energy (EE) and cost by 16.98%, 36.1%, and 67.53% respectively than full depth PVA fiber reinforced slab (HECC1). PI method indicated that HC-SL6 slab members most preferable for flexural strength capacity, ultimate load, environmental and economical aspects.

ULTIMATE STRENGTH OF CLAMPED R.C SQUARE SLABS WITH CENTRAL SQUARE OPENING UNDER COMBIEND BENDING AND MEMBRANE ACTION

Based on the flow theory of rigid-plastic bodies, a method is developed for assessing the ultimate strength as well as determining the post yield behavior of uniformly loaded R.C square slabs with central square opening which have all edges restrained against rotation and lateral movement . The method takes into account the significant effects of membrane forces which are usually induced in the plane of the slab along sagging and hogging yield lines as the slab deflects. Considering equilibrium and compatibility of the deformed slab element, load-deflections relations are derived starting from the initial compressive membrane action up to tensile membrane and full-depth cracking at large deflection. The solution shows that axially restrained slabs can sustain loads far beyond those predicated by Johansen's yield line theory and the enhancement in load is greatest for thinner slabs having lighter reinforcement and smaller opening. On the basis of an estimated deflection, theoretical ultimate loads are found comparable with those of existing experimental tests. A theoretical study of the maximum yield load reveals a promising saving in reinforcement for using stronger concrete. For an interior square panel with central square opening, such saving in reinforcement could be as high as 48% if the panel is lightly loaded, and 25% for a panel under moderate loads.

A BRIEF REVIEW OF STEEL FIBER SELF-COMPACTING CONCRETE IN RIBBED SLAB

The use of Steel Fiber Reinforced Self-Compacting Concrete (SCFRC) as structural elements is seen as favorable alternative to solve typical issues of complex reinforcing spacing and compaction in normal reinforced concrete. The primary benefit of SCFRC is that it can be easily poured in-situ, filling corners of formwork and gaps between bars of reinforcement with its own weight. SCFRC's structural performance is constantly being investigated because of its superior engineering and mechanical properties. Steel fibers added to the mix improved the hardened properties of self-compacting concrete in terms of tensile strength, ductility, toughness, energy absorption capacity, and cracking resistance. This study reviews previous research on SCFRC performance in slab structures with an emphasis on flexural performance. Thus, the knowledge could provide guidelines for academia and industry players on the structural and materials behavior of the slab elements.