Waffle Slab Research Articles

Design and Analysis of Ribbed Raft Foundation Resting on Swell-Shrink Soils

Expansive soils shrink and swell with drying and wetting cycles. The shrink-swell capacity of expansive soils can result in differential movement beneath foundations which is a very common cause of foundation problems. Ribbed slab, often called waffle slab, is one of the efficient and inexpensive foundation solutions for use under light structures resting on shrink-swell soils. This paper presents a numerical analysis that is used to calculate displacement and internal forces in ribbed slab foundations resting on swell/shrink soil. The stiffness of the ribbed slab is modelled as an equivalent flat slab of constant thickness and the straining actions are calculated for the case of central heave. A parametric study of the effect of beam dimensions and rib spacing is performed to assess the optimum configuration. Dimensioning of the waffle slab system; slab thickness, depth and width of beams and spacing, is performed according to the Egyptian Code of Practice for the design of concrete structures. The results show that beam depths of 0.4 m and 0.45 m were safe and recommended under this condition of heave scenario. All beams with depths of 0.3 m cannot resist the resulting bending moments, While beams with 0.35 m depth are only safe when the beam width is not less than 0.2 m.

Eco-friendly and economically optimal design model (EEODM) to reduce the CO2 emissions and the cost of long-span waffle slabs

As the emission of CO2 is directly proportional to the nature of the materials used in the construction of buildings, an eco-friendly economic design is required for waffle slabs used in large buildings such as stores, shopping malls. In this study, a multi-objective optimization design model, denoted as an eco-friendly and economically optimal design model (EEODM), is proposed to reduce the CO2 emissions and costs of long-span waffle slabs. The developed model was analyzed to determine the change in CO2 emissions and costs with respect to design variables in 20 types of long-span waffle slabs. Based on the results of the analysis, CO2 emission efficiency analysis (CEEA) and cost-efficiency analysis (CEA) are proposed as the new qualitative scales to determine environmental and economic feasibility, respectively. Through CEEA and CEA, a new design standard is proposed to overcome the limitations of existing waffle forms. To verify the applicability of the EEODM, the model proposed in this study was applied to the actual waffle slab of Gimpo International Airport in Korea. The results indicate that the two proposed waffle forms reduced CO2 emissions and costs compared to the existing sections of the airport.

Decision Making and Predicting the Cost for the Optimal Structural System of Multi-Story Buildings

There are numerous structural lateral systems used in multi-story buildings design such as the shear wall, frame system, framed with core, dual systems and superframes, etc. Additionally, the system of slabs such as (Solid Slab, Flat Slab, Flat plates, Hollow blocks, ... and Waffle Slabs). Generally, the structural systems of multi-story buildings are considered to be different types. Multi-story buildings are commonly used in residential, commercial and administrative projects; therefore, determining the structural system with minimum cost is the top priority of the structural designer. This research aims to introduce recommendations for the optimum structural system for a multi-story Reinforced Concrete (R.C.) building from a perspective of direct cost to help decision-makers in the preliminary design for choosing the optimum structural system. This paper outlines the development of charts to predict optimal structural system costing, using the status of early conceptual design as the charts input. In order to achieve that goal, a parametric study was carried out using 27 RC buildings with several stories ranging between 5 to 50 floors and grid spacing ranged between 6.0 to 12.0 m. Three floor systems were considered which are solid, ribbed and flat slabs.

Experimental Investigation of Flexural Behavior of Steel–UHPC Composite Beam with Waffle-Slab System

Abstract The flexural behavior of steel-ultrahigh performance concrete (UHPC) composite beams with waffle slabs (SUCBWS) was investigated through experiments. The effects of design parameters, incl...

Accelerated testing of super lightweight UHPC waffle deck under heavy vehicle simulator

A super lightweight deck can enhance load rating and functionality of a bridge, especially those identified as structurally deficient. This study was aimed to develop and experimentally validate a novel bridge deck as an ultra-lightweight low-profile waffle slab of ultra-high-performance concrete (UHPC) with either carbon fiber reinforced polymer (CFRP) or high strength steel (HSS) reinforcement. The proposed system lends itself to accelerated bridge construction, rapid deck replacement in bridges with load restrictions, and bridge widening applications without the need to replace girders. Performance and failure modes of the proposed deck were initially assessed through extensive lab experiments and finite element analysis, which together confirmed that the proposed deck panel meets the AASHTO LRFD requirements. The proposed deck system is not susceptible to punching shear of its thin slab and fails in a rather ductile manner. To evaluate its long-term performance, the system was further tested under the dynamic impact of wheel load at the Accelerated Pavement Testing (APT) facility of the Florida Department of Transportation using a Heavy Vehicle Simulator (HVS).

Behaviour of waffle slab

Waffle slabsare lighter in weightthan an equivalent solidslabwhich helps in diminishing the weight with its voids. This study is performed to investigate the behaviour of thewaffle slab. Waffle slab types of construction are economical for building where there are long spans, over between 5 m and 6 m with light to moderate live load. It reduces slab weight by reducing amount of concrete. The waffles slab less in dead load and high in load caring capacity. This would allow the structural designer to reduce the size of column, footing and other load bearing elements. For literature review, it is observed with variation in spacing, depth of beam and analytical results of waffle slabare studies. In this project work the waffle slab system with various spacing of grid beams are casted and tested for the load carrying capacity.

Behaviour of Flat Slab, Waffle Slab, Ribbed & Secondary Beam in a multistorey Building under Seismic Response: A Review

Behaviour of Flat Slab, Waffle Slab, Ribbed & Secondary Beam in a multistorey Building under Seismic Response: A Review

Effect of the transversal-spacing of stirrup-legs on the behavior and strength of shallow concealed RC beams

PurposeShallow concealed reinforced concrete (RC) beams (wide beams) make parts of a structure and are used in the construction industry, especially in ribbed and waffle slab systems. They are designed based on the requirements and provisions of structural codes of practice, which are applicable for shallow dropped RC beams (narrow beams). The main concern in regard to the behavior of these shallow concealed RC beams is transversal-spacing of stirrup-legs across their width. This paper aims to investigate the transversal-spacing of stirrups-legs (Sw) for two shallow concealed RC beams, namely, WB-SC and WB-EC.Design/methodology/approachThe beams are tested under a three point-loading system. Their design has been performed to the SBC304 for beam WB-SC (Saudi Building Code for concrete structures) and comparison to EC2 for beam WB-EC (Eurocode-2 for concrete structures) is addressed in terms of flexural and shear strength design requirements. Experimental behavior and results of both beams are analyzed and conclusions are provided; also, a comparison of these codes is performed. Both beams had dimensions of 3,400 mm length, 700 mm width and 350 mm height.FindingsExperimentally, beam WB-SC failed in flexure while beam WB-EC failed shear. The investigation concludes in favor of a safer design for SBC304 Code compared to EC2 Code for designing shallow concealed RC beams.Originality/valueThis study recommends that the transversal-spacing of stirrups-legs of these beams has an influence on their strength and behavior and should not exceed the lesser of 0.56(d) or 170 mm (6.7 in.).

Selection of optimum structural roof system in Saudi Arabia for a conference hall without interior columns in terms of cost and feasibility

The major challenge in civil engineering has been and will always be the design and construction of structures that fulfill the technical and investment market requirements for the criteria of cost, reliability, maintenance, environmental sustainability and aestheticism. This study deals with structurally analyzing and designing a 20 m × 40 m conference hall without interior columns contained within a two story building using the structural floor systems of concrete waffle slab, composite steel concrete and hollow core slab. The Design was carried out with adherence to several design manuals and Saudi building codes. The comparing between the three floor systems in terms of cost & feasibility was carried out. Throughout the study, several information and charts were produced regarding the systems’ comparison factors of structural deflection, depth on foundation, systems’ cost, aestheticism, and contractibility & maintenance. Finally, the results concluded that the hollow core slab system is the most technically superior and feasible alternative in the proposed case. Its relatively low cost, low structural depth and deflection mark it as ideal for long span heavily loaded structures.

A New Hybrid Algorithm for Cost Optimization of Waffle Slab

Abstract In this paper, we have developed an efficient hybrid meta-heuristic algorithm for structural cost optimization of a waffle slab and have also solved the relevant optimization problems. The cost of the waffle slab is considered to be the objective function, and the design is based on the American Concrete Institute’s ACI 318-08 standard. This algorithm utilizes the recently developed mouth-brooding fish (MBF) algorithm as the main engine and uses the favorable properties of the colliding bodies optimization (CBO) algorithm. The performance of this algorithm is compared with MBF, CBO, harmony search (HS), particle swarm optimization (PSO), democratic particle swarm optimization (DPSO), charged system search (CSS) and enhanced charged system search (ECSS). The numerical results demonstrate that the proposed algorithm can construct promising results and has merits in solving challenging optimization problems.

Numerical and theoretical research on flexural behavior of steel-UHPC composite beam with waffle-slab system

Based on the experimental study on six steel-UHPC composite beams with waffle slab (SUCBWS), a three-dimensional finite element model was proposed to analyze the flexural behavior of SUCBWS. Then the applicability of finite element model was validated against the experimental results. A subsequent parametric study was performed to investigate the effects of yield strength of steel, ratio of rib height to upper panel thickness, transverse reinforcement ratio and layout of ribs on the flexural behavior. Results show that the reduction of thickness of upper panel for waffle slab will significantly weaken its integrity and increase the risk of longitudinal splitting failure by comparing with reducing the number of ribs. The waffle slab with low ribs should be adopted as the bridge deck. The increase of transverse reinforcement ratio has little effect on improving the ultimate flexural capacity, while it is obvious for improving the ultimate deformation capacity. The minimum transverse reinforcement ratio of 0.5% is suggested. The contribution of ribs is small for flexural capacity but is large for ensuring ultimate deformation capacity. Finally, the calculation method of ultimate flexural capacity was proposed. The comparison of theoretical, experimental and numerical results revealed the good accuracy of predictions indicating that the actual behavior of SUCBWS was reasonably reflected by the calculation method.

Experimental and numerical investigation of steel–ultra-high-performance concrete continuous composite beam behavior

This article proposes a new kind of continuous composite beam that consists of steel box-girder and ultra-high-performance concrete waffle slab. The ultra-high-performance concrete helps increase the ultimate capacity and span of structure while reducing the risk of cracking that occurs with ordinary concrete. In order to investigate the mechanical properties of this new type of composite structure, two scaled specimens were designed and tested. One was a steel–ultra-high-performance concrete continuous composite beam, whereas the other, as a control specimen, was a prestressed steel-concrete continuous composite beam. The test results indicate that the bending capacity of steel–ultra-high-performance concrete continuous composite beam is 1.2 times that of steel-concrete continuous composite beam; the cracking strength of steel–ultra-high-performance concrete continuous composite beam is larger than 20 MPa, much higher than the conventional one; the crack development pattern of steel–ultra-high-performance concrete continuous composite beam has its own characteristics, and the cracks appeared in ultra-high-performance concrete slab dominated by micro-cracks with smaller length are numerous and intensive. A finite element model was developed to predict the behavior of steel–ultra-high-performance concrete continuous composite beam. Comparing the numerical and experimental results indicates that, generally, the numerical model can simulate the structural behavior of steel–ultra-high-performance concrete continuous composite beam reasonably. Based on the numerical model, a series of parameter analyses were performed, which indicate that the strength grade of steel, web, and bottom plate thickness play an important role in improving the bending capacity of steel–ultra-high-performance concrete continuous composite beam; the axial tensile strength of ultra-high-performance concrete, rib, and top plate height of ultra-high-performance concrete slab can enhance the bending capacity to a certain extent.

Experimental and Analytical Study on the Vibration Performance of U-Shaped Steel-Concrete Composite Hollow Waffle Slab

The large-span floor system being lightweight with low frequency and low damping is prone to suffer severe vibration under human excitations. In this research, the vibration performance of an innovative large-span U-shaped steel-concrete composite hollow waffle (CHW) slab was studied based on field testing and theoretical analysis. First, the modal properties of CHW slab including mode shapes, frequencies, and damping ratio were captured by on-site tests and validated by the finite element method, indicating the CHW slab is a low-frequency floor system with a low damping ratio. Second, the vibration responses of CHW slab under heel-drop and jumping excitations were studied considering the impacts of spatial position, tester number, and activity types. Third, the CHW slab shows excellent vibration serviceability proved by the frequency, accelerations, and human perceptions threshold with the current codes. Meanwhile, the paper gives appropriate threshold values for the CHW slab under impulsive excitation. Finally, the natural frequency formula for the CHW slab derived by the Rayleigh–Ritz energy method agrees well with the measurements.

Analysis of ribbed & Waffle Slabs with Design Loading Condition under Different Boundary Conditions

Analysis of ribbed & Waffle Slabs with Design Loading Condition under Different Boundary Conditions

Influence of concrete cover in the service life of a newly built reinforced concrete structure: a case study

Structural collapse of civil engineering structures at an early age, as for instance bridges, tunnels and buildings, can present a high impact on economic issues of cities around the world, which emerges the necessity of early corrective maintenance and deep interventions. In this context, recent years, new studies and strategies focused on the durability of reinforced concrete structures have been developed. This case study aims to estimate the residual service life of a newly constructed reinforced concrete structure based on in-situ measurements of concrete cover, performed in 1662 points of columns and slabs to assess the impact of possible divergences between designed and as-built structural elements. Results show that a combination of concrete cover lower than the minimal and water/cement ratio higher than the maximum specified by Brazilian standards resulted in service life under 50 years in 53.8% of the inspected points of columns and 100% of the inspected points of waffle slabs. Even inspected points with concrete cover higher than the minimum requirement of the Brazilian design standard resulted in residual service life under 50 years. In critical points, the estimated residual service life resulted in 9.5 years for columns and 20 years for waffle slabs, which is far below the expected performance for a newly built reinforced concrete structure.

Computational modeling of flat slabs: Influence of ribs and flexural reinforcement on shear strength

Abstract A greater number of structures are being built with flat reinforced concrete slabs because they offer several advantages. However, many designers are still unsure about the type of slab that has the best structural performance and which building codes provide the best strength estimates. This study presents nonlinear computer simulations of 16 flat reinforced concrete slabs under symmetrical punching: 4 solid slabs, 4 waffle slabs with wide beams, and 8 waffle slabs with different numbers of ribs supported in the solid area of the slab. Geometric longitudinal reinforcement ratios ranged from 0.45% to 1.97%. The results showed that solid and beamed slabs are more resistant, and normative estimates overestimate their strengths, while the opposite outcome was found for waffle slabs, whose estimates provided in the codes were rather conservative. The most accurate code was EC2, followed by ACI 318 and NBR 6118.

Analysis and design of commercial building with different slab arrangements using ETABS

Earthquake plays an influential role in analysis and designing of structures. Analysis is the process of determining the behaviour of structure under specified load combinations. Design is the process of finding appropriate specifications for the structure. Manual analysis and design of structure would consume a lot of time. By using software, analysis and design of any structure can be done quickly. The principle purpose of this work is to analyse and design a commercial building with different slab arrangements, i.e., Conventional slab, Flat slab with drop panels, Grid/ Waffle slab, and building with load bearing wall. A commercial building is one in which at least 50 percent of its floor space is used for commercial activities. The effect of seismic and wind forces on buildings with different slab arrangements have been analysed by utilizing ETABS software. ETABS is an engineering software product which is utilized for analysis and design of structures. Analysis and design are done as per IS 456-2000 code book. M30 grade of concrete and Fe-500 steel is adopted. Load combinations are taken as per IS: 875-part 5 (2015) code book. Live loads are taken as per IS 875-part 1. Wind speed of 55 m/s and earthquake zone 5 is adopted for analysis. Load combinations of 1.2(DL + LL + EQ) and 1.5(DL + LL + WL) are considered. There are several concerns which affect the performance of structure from which storey drift, base shear and storey displacement play a crucial role in finding the behaviour of structure against the wind and seismic loads. Results are conveyed in form of tables, bar charts. Storey displacement increased with storey height. The result shows that building with grid slab is stable and economical, contrasting to all other slab arrangements used in the building analysis against wind and seismic loads.

Assessment on Human Comfort Criteria of Tall Building under Dynamic Wind Loading

The tall, light, flexible buildings may have large oscillating motions induced by wind or other causes that affect the comfort of the occupants. Wind induced motion in buildings may result in excessive vibrations such vibrations can cause discomfort conditions for occupants or damage to non structural elements. So it is essential to analysis the dynamic behavior of the tall building under the wind excitation which influences the human comfort. The purpose of present study is to anysied the range of human perception criteria associated with human comfort that is applied for serviceability limit state design. The design criteria were proposed based on the subjective perception test. The guideline for evaluating the acceptability of wind-induced tall buildings motions was defined by the expected value of motion perception acceleration. In this Project, human comfort condition of a tall building under wind excitation is assessed using estimation of peak acceleration by using Indian standard code IS 875(part3) :2015. Considering Four different Framed Tubes tall building circular structure having a G+20, G+30, G+40, and G+50 with different condition i.e. Normal Slab, Secondary Beam, Waffle Slab & Ribbed Slab are taken. Typical circular floor is 50 m in diameter and symmetrical in plan in both major directions. Then using ETABS-2013 software maximum displacement is evaluated using dynamic wind analysis of building by applying the gust factor method. With the help of maximum Displacement Peak acceleration will be calculated using is IS-875(part3); 2015 for different Framed Tubes structure conditions and modes of building. The peak acceleration obtained in the analysis is compared with the reference data given by Smith. S.B. and Coull book and human comfort perception level is calculating for Indian tertiary of the described location of India from which assessment of effective tall building under dynamic wind load is anysied.

Numerical analysis of torsional tangent rigidity of reinforced concrete waffle slab

Abstract This research work deals with the analysis of torsional tangent rigidity of reinforced concrete waffle slabs by comparisons of the numerical analysis with results of experimental tests, with calculations performed using the ATENA program. This program was specially developed for the calculation of reinforced concrete structures, considering the physical and geometric nonlinear analysis using the finite element method. Numerical analysis considered the tensile strength of the concrete and consequently the fracture energy. Numerical situations were tested to obtain the calibration of the numerical analysis with the laboratory tests. After the calibrations, the results were extrapolated to extreme situations to infer tangent torsion rigidity in new situations. It is concluded that, for waffle slabs, near the rupture, the torsional tangent rigidity should be 5% of the torsional tangent rigidity to the initial torsion. In service, considering one third of the total breaking load, the torsional tangent rigidity should be 85% of the torsional tangent rigidity to the initial twist. This great torsional tangent rigidity in service is another parameter that guarantees the structural efficiency of the waffle slabs and can be used in the most diverse applications of structural engineering.

Shear behaviour of steel-UHPC composite beams in waffle bridge deck

This paper firstly proposed the steel-UHPC composite beam in waffle bridge deck system. Then, the shear behaviour of steel-UHPC composite beams in waffle bridge deck system was studied through two-point loading tests on six large scale specimens. The influences of shear span, depth of the rib, and width of the UHPC waffle slab were studied in this testing program. The experimental results reported the typical flexure and shear mode of the composite beam, and their respective ultimate strength behaviours in terms of load versus deflection (or strain) curves and load-transferring mechanism. The test results also showed that shear spans changed the failure mode of steel-UHPC composite beams. The height of the rib in the waffle slab acted less importantly than the thickness of slab on improving the shear resistance of composite beam. Theoretical models were also developed to predict the ultimate bending and shear resistances of steel-UHPC composite beams. The validations of the predictions against reported six test results showed that the developed theoretical models offered conservative estimations on shear resistance, but more accurate estimations on flexural bending resistance.