Concrete Hollow Core Research Articles

Second life for pre-stressed concrete hollow core slabs – time to act

The construction sector contributes to approximately 50% of global carbon dioxide emissions and natural resource consumption, along with generating a significant amount of landfill waste. Thus, there is an urgent need to actively involve our professional community in fostering real environmental change. Embracing circularity in construction presents significant opportunities for decarbonization, particularly in the context of prestressed precast concrete structures. This paper explores the potential for reusing prestressed hollow core slabs already built-in, as well as the principles of designing for future dismantling and reassembly. A second life for hollow core slabs is possible, as has already been confirmed by practical realisations in the Netherlands, Sweden and Finland.

Post-Tensioned Hollow-Core Concrete Slabs with Unbonded Tendons for Truck Scale Platforms: Design Assumptions and Tests.

At Cracow University of Technology, attempts were made to develop national truck scale platforms with a capacity of 60 tons, made from prestressed concrete. For this work, we designed slabs partially prestressed with unbonded tendons featuring a cross-section of 1.00 × 0.28 m and a span of 5.94 m. To reduce the weight of the slabs, four channels made from commonly used ø110 × 2.2 mm PVC pipes were used. In this way, we created post-tensioned hollow-core slabs. Due to the unpredictable behavior of slabs operating in a cracked state under a repetitive load, two slabs were subjected to cyclic loads amounting to 1,000,000 cycles with different load values. This paper presents the basic design principles and design details of the slabs, as well as the methodology and results of the research conducted. Lastly, we provide appropriate conclusions directed at further optimizing the slabs.

Static and dynamic load test on concrete hollow-core slab bridge

In this paper, dynamic and static load test were carried out on a multi-span reinforced concrete simply supported hollow core slab bridge in Shenyang, Liaoning Province. Through the static load test, the quality and reliability of the project are evaluated, and the results show that under the action of 0.88 times of highway-classⅠload, the deflection and strain check coefficients of the control section of the tested condition are less than 1, which meets the specification requirements, and the measured relative residual deformation and relative residual strain are less than 20%, and the bridge structure is basically in the elastic working state. And combined with the finite element analysis model, the comparison between measured data and calculated data is carried out. Through the dynamic load test, the self-oscillation frequency and damping ratio of the superstructure were tested, and the results showed that the measured damping ratio was 0.690%, the first-order measured vibration pattern conformed to the variation rule of the vibration pattern of the simply supported girder bridge, and the measured self-oscillation frequency was 13.594 Hz, and the measured self-oscillation frequency (fundamental frequency) was greater than the calculated frequency, and the structural actual stiffness was greater than the theoretical stiffness, and the working condition was good. This study is of great significance for the assessment of bearing capacity and quality control of concrete hollow core slab bridge, and provides a useful reference for bridge design and operation.

Evaluation of Maximum Shear Strength of Prestressed Concrete (PSC) Hollow Core Slab (HCS)

In this study, four-point load tests were conducted to evaluate the shear performance of factory-produced precast prestressed concrete hollow core slabs (HCS) assembled on-site. The test specimens were fabricated using compression molding and comprised six samples, with variables being the presence or absence of topping concrete and the shear reinforcement. According to the experimental variables, experiments were conducted using simple support beams to evaluate the shear performance and ultimate strength of HCSs. The results showed that HCSs, regardless of whether they included topping concrete or not, exhibited average values of shear strength more than 10% higher than the factored shear strength specified by concrete structure standards, confirming that these materials satisfy existing design standards. According to current standards, the overall reinforcement length should be increased to meet the minimum shear rebar placement requirements. However, the nominal shear strength of PS concrete hollow slabs exceeded the hollow design, with the ratio of experimental results ranging from 1.26 to 1.87 on average, satisfying the required performance.

Application of Artificial Neural Networks to Numerical Homogenization of the Precast Hollow-Core Concrete Slabs

The main goal of this work is to combine the usage of the numerical homogenization technique for determining the effective properties of representative volume elements with artificial neural networks. The effective properties are defined according to the classical laminate theory. The purpose is to create and train a rapid surrogate model for the quick calculation of the mechanical properties of hollow concrete slabs. First, the homogenization algorithm was implemented, which determines membrane, bending and transverse shearing properties of a given parametrized hollow-core precast slab reinforced with steel bars. The algorithm uses the finite element mesh but does not require a formal solution of the finite element method problem. Second, the learning and training artificial intelligence framework was created and fed with a dataset obtained by optimal Latin hypercube sampling. In the study, a multilayer perceptron type of artificial neural network was used. This allows for obtaining rapid calculations of the effective properties of a particular hollow-core precast slab by using a surrogate model. In the paper, it has been proven that such a model, obtained via complex numerical calculations, gives a very accurate estimation of the properties and can be used in many practical tasks, such as optimization problems or computer-aided design decisions. Above all, the efficient setup of the artificial neural network has been sought and presented.

Comparative Study of Numerical Methods for Predicting Crack Propagation in Reinforced Concrete Hollow Core Slabs

Hollow core slabs are commonly used in prefabricated building construction and are calculated and constructed using gravity loads. The dead loads of the structure are reduced by using this slab system. Different criteria, such as the initiation and propagation of cracks in the hollow core slab, are used to analyze these slabs. Fracture mechanics is the basis for studying crack propagation. The present study was conducted to analyze the propagation of cracks in hollow core slabs under common loading conditions using the finite element method and numerical modeling to analyze cracks in reinforced concrete members. This research is theoretically conducted using finite element software. This research takes into account the potential varieties of cracks in concrete slabs. Slabs should consider all three types of cracks, which are shear, flexural, and flexural-shear cracks obtained from the reference test. Two Contour integral and XFEM methods are used to analyze cracks in Abaqus software. To validate and control the modeling process, the laboratory results of the research of Ibrahim N. Najma, Raid A. Daudb, and Adel A. Al-Azzawi. December 2, 2019, has been used. The outcomes of this study showed that the probability of the formation of a flexural-shear crack in the slab is higher than in other crack forms.

Degree of composite action of steel beams with precast concrete hollow core slabs

Different construction challenges followed by harsh environmental conditions triggered the human intention to precast composite structures. The precast concrete hollow core (PCHC) slabs have been popular, especially for multi-story long-span composite structures. In comparison to conventional solid concrete slabs, they have the advantages of being more lightweight, fire-resistant, soundproof, and cost-effective. However, the composite action between the steel beams and PCHC slabs is neglected in the design codes. This paper aims to investigate the composite action between the PCHC slabs and steel beams through an experimental study. Two full-scale flexural tests were performed on specimens of 203 cm and 254 cm PCHC slabs connected to the steel beam via 19 mm diameter shear studs. Instrumentations and data acquisition systems recorded the failure modes and crack formations. Also, the digital image correlation (DIC) technique was applied to capture the neutral axis position during the loading process. Finally, the degree of composite action (DCA), an important parameter to describe the structural behavior of the composite beam, was calculated based on the analytical and experimental bending moments of the specimens.

Test and analysis on in-plane shear behavior of precast concrete hollow core slabs

Precast concrete hollow core (PHC) slabs are mostly used in industrial and civil buildings because of the low weight and high efficiency of construction. The previous researches are mainly focused on the out-of-plane bending and shear behavior of PHC slabs. However, the in-plane shear behavior of the PHC slabs with high-strength tendons is not fully understood yet. In this regard, to investigate the in-plane shear behavior of PHC slabs, shear tests were conducted on a new long PHC slab with high-strength tendons and a new spliced slab in the present paper. The spliced slab was composed of two PHC short slabs with U-type bars, post-pouring concrete and anchorage bars. Subsequently, finite element models were established and validated by the test. Parametric analysis was conducted on the spliced slab to study the effect of the reinforcement ratio of tendons, concrete strength, tendon prestress, position of loading point, etc. Furthermore, based on the deep beam theory of single generalized displacement, the modified theoretical formulas on the in-plane initial stiffness of the specimens were illustrated. The results show that the mechanical behavior of the spliced slab was better than that of the long slab, including shear capacity, energy dissipation capacity and ductility. The initial stiffness and shear capacity of the spliced slab improved obviously with the reduction of the distance between the supports. The difference between in-plane initial stiffness of the PHC slab obtained from the modified theoretical formulas and that obtained from experiment are within 5%, which means the proposed formula can predict the in-plane initial stiffness of the PHC slabs well. This may provide a reference for the application of the long PHC and spliced slabs in engineering.

Structural Behavior of Reinforced Concrete Hollow Core Slabs Cast with Self-Compacting Concrete Containing Recycled Concrete as Coarse Aggregate

This paper investigates the possibility of recycled aggregate use in concrete slabs with hollow cores. The main variables considered in the experimental study for the slabs were the recycled aggregate percentage and the hollow core number. Six slabs with dimensions of (1000 × 500 × 120) mm was fabricated and tested. The results showed that the addition of recycled aggregate in the concrete slabs affected the ultimate strength, ductility, and energy absorption of the concrete members. An increase of the recycled aggregate percentage to 25 % decreased the ultimate strength capacity by 3.54 %, but the increase of recycled aggregate to 50 % led to a decrease in the ultimate strength of about 6.64%. The existence of a hollow core reduced the cracking and ultimate load capacity of the RCA slabs, and this reduction was according to the core number which the fabrication of more cores caused more decrement. The ductility and energy absorption were decreased when the replacement ratio of the recycled aggregate increased. Also, the core number affected the ductility and energy absorption. The energy absorption was the most property affected by the core number increase which caused an average reduction of 71.5 % when the core number increased from two to three hollow cores.

Fire resistance and associated failure modes of axially restrained hollow core slabs

When a severe fire occurs in the central part of a large hollow core slab floor, the thermal expansion of the affected floor members will be highly restrained by the stiffness of the surrounding structure. The present paper presents the development of a numerical model to evaluate the structural performance of precast concrete hollow core slabs exposed to fire, taking into account the interaction with the surrounding structure and how it affects the fire resistance and failure mode. The performance of the model is validated against fire tests reported in the literature. Subsequently, the model is employed to evaluate the influence of various degrees of restraint on the fire resistance of three hollow core slab sections, with depths ranging from 200 mm to 500 mm. The results indicate that restrained thermal expansion can significantly enhance the fire resistance of concrete hollow core slabs with low span-to-depth ratios. Conversely, in hollow core slabs with a high span-to-depth ratio, the restraint provided by the surroundings can considerably impair the fire performance. Additionally, it is shown that the failure mode of hollow core slabs can change from ductile bending failure to a brittle shear failure mode in the presence of axially restraining boundary conditions.

Capacity and failure modes of restrained hollow core slabs taking into account compressive membrane action

AbstractThe formation of compressive membrane action in restrained precast concrete hollow core slabs is investigated, and how it affects the load bearing capacity and failure mode under excessive loading. To this end, attention is oriented to a recently completed experimental campaign specifically aimed at quantifying this phenomenon in real‐scale hollow core slabs. The outcomes of this experimental campaign are then analyzed using a validated finite element model, to further study the effects of compressive membrane action on the structural behavior of hollow core slabs. From the numerical evaluations, it can be concluded that the ultimate capacity and failure mode of restrained hollow core slabs strongly depend on the restraint conditions, as well as the span‐to‐depth ratio. The results also indicate that in some cases the failure is caused by crushing of concrete in the top flange, which is typically not observed in case of simply supported boundary conditions. Additionally, the influence of the inherent uncertainties associated with material properties and geometry on the ultimate capacity and failure mode of restrained hollow core slabs is investigated. Probabilistic model evaluations are performed for a wide range of boundary conditions. The results indicate a very high influence of the uncertainty on the concrete tensile strength on the membrane action in precast hollow core slabs.

Prestressed hollow-core slabs performance at high temperatures- A review

Pre-stressed concrete hollow core slabs (HCS) are now progressively usedin commercial, industrial, and residential buildings due to their sustainability,affordability, and adaptability. The performance of HCS units subjected to fire isparticularly difficult and is attributable to their unusual cross-section, whichfeatures voids. Numerous investigations were executed on HCS at hightemperatures concerning the crucial temperature and failure mechanisms of bothconcrete and prestressing steel. Fire performance is influenced by a number ofvariables, including support condition, concrete aggregate type, slab thickness, fireinsulation and cover thickness for reinforcement, spalling accessibility, void coresand size, and firing methodology. While a number of these variables have receivedextensive research, some have been noted as potential contributory reasons forfailure, while others have received relatively little attention. This paper summarisesnumerous experimental, numerical, and analytical studies about the attitude of HCSvulnerable to fire in addition the building standards limitations to provide a valuablereference for future researchers

A NOVEL STRATEGY FOR SLIM‐FLOOR FIRE PROTECTION

AbstractThis paper presents a novel slim‐floor configuration which consist of an I‐section steel profile welded to a wider bottom steel plate with an insulation layer of 5mm thick placed in between the two. The insulation layer is made up of a flexible and non‐combustible material, which protects the I‐section profile from the temperature rise through its bottom surface. Besides, this insulation layer remains protected from external agents with no need of maintenance because it is placed in the cavity created on purpose between the bottom plate and the lower flange of the steel profile thank to the weld between them. This new slim‐floor configuration is currently right‐protected by the Spanish Office of Patents and Trademarks with the reference number P201930438 and has been tested in the Universitat Politècnica de Valencia testing facilities to assess its thermal behaviour in fire. Specifically, the specimen was tested using an electric furnace where the slim‐floor is placed at the top surface. Therefore, the composite beam is exposed to the heat source only from the bottom surface, as it is the case in real fire scenarios. Moreover, the experimental campaign includes also a common slim‐floor specimen, without the insulation layer, in order to compare their thermal behaviour. The steel parts used in all the test specimens were grade S355, having a nominal yield strength of 355 MPa, the nominal compressive strength (cylindrical) of the cast in‐situ concrete was 30 MPa and the precast concrete hollow core slabs were manufactured with 45 MPa nominal compressive strength (cylindrical). In turn, the embedded reinforcing bars were grade S500, with 500 MPa nominal yield strength. The first experimental results have shown that the temperature gap between the bottom steel plate and the lower flange of the steel profile can reach up to 200°C. This impressive thermal gap delays the temperature rise along the I‐section steel profile which produces a significant improvement on the composite section fire resistant time, up to 90 or 120 minutes. Additionally, it should be highlighted that the observed improvement on the cross‐section thermal behaviour has been achieved using a novel configuration which no need maintenance in contrast with the common external protection systems using intumescent coating or other fireproofing materials.

A Method of Evaluating the Destruction of a Reinforced Concrete Hollow Core Slab for Ensuring Fire Resistance

Fire tests of reinforced concrete floor slabs do not allow the detection of the onset of the boundary state due to loss of entirety because blocks are installed on the unheated surface to reproduce the design load. This prevents the formation of cracks through which toxic combustion products, smoke, and temperature spread can penetrate. Determining a building structure’s actual fire resistance limit was fixed at the onset of any fire resistance boundary state. It was proven that calculation methods for fire resistance assessment have significant advantages over experimental methods. To reduce the number of finite elements for a rational calculation of the fire resistance assessment of a reinforced concrete hollow core slab, a geometric model of 1/4 of this structure was built. The possibility of visualizing the studied structure at full scale was realized when obtaining the calculation results. The stress-strain state of the studied structure was evaluated based on the thermal and mechanical loading results applied to the reinforced concrete hollow core slab. Thus, the work’s objective was achieved based on the calculation experiments’ results. A methodology was developed for calculating the destruction of a reinforced concrete hollow core slab while assessing its fire resistance. Scientific fundamentals for determining the onset of the boundary state of loss of entirety were developed. The proposed methodology allowed for a reliable assessment of the fire resistance of such structures.

Structural reliability of hollow core slabs considering compressive membrane action

Compressive membrane action can considerably improve the load bearing capacity of concrete slabs and beams in case of excessive loaded due to an accidental event. Currently, only limited research has been focusing on compressive membrane action in prestressed concrete elements, or on concrete elements with large cavities, such as precast concrete hollow core slabs. Therefore, a novel real-scale test setup has been developed in order to assess this effect in precast hollow core slabs, and how it can enhance the load-carrying capacity in accidental events. In parallel with these tests, a numerical finite element model has been developed in order to perform a more detailed structural analysis of this phenomenon, and to study the influence of various input parameters. The details of this test setup are briefly explained, and some relevant experimental test results are provided. Considering the experimental findings and validated numerical model, this contribution aims to quantify the influence of compressive membrane action on the structural reliability of precast concrete hollow core slabs. To this end, probabilistic models for the most important material and geometric variables are gathered, and the structural reliability is assessed using Latin Hypercube sampling. Overall, the results indicate that considering the formation of compressive membrane action strongly influences the variability of the ultimate load-carrying capacity of precast concrete hollow core slabs.

Flexural behavior of precast concrete hollow-core slabs with high-strength tendons

Precast concrete hollow core (PHC) slabs have been widely used in brick and concrete structures of rural buildings due to their economic and rapid construction in China. A new PHC slab with high-strength tendons and spliced slab made of the short slabs were proposed in this paper. To investigate the flexural behavior of the slabs, full-scale tests were conducted on three PHC slabs, including one long slab and two spliced slabs with side beams. In detail, the spliced slab was assembled by two short slabs through U-type bars, anchorage bars, and post-pouring concrete. The mechanical properties of specimens were evaluated including the failure modes, strain of concrete and bars, flexural capacity and deflection. The tests results shows that the flexural performance of the spliced slab is close to that of the long slab. Subsequently, finite element models were established and validated by the test data. Based on the validated models, an additional specimen made up of long slab and side beams, was studied to further verify the reliability of the spliced slab. And parametric analysis were carried out on the spliced slab to investigate the influence of prestress of tendons, diameter of tendons, concrete strength, etc. Moreover, the cracking and failure moment of the slabs were calculated by the formulas of GB50010 and ACI318, respectively. The calculated results were compared with the test and simulation results. The results proves that the prediction values calculated by the codes on the flexural capacity of the spliced slab is not conservative. Therefore, considering a reduction factor to correct the results calculated by the codes is necessary.

Tension stiffening in reinforced concrete hollow core slabs

Tension stiffening in reinforced concrete hollow core slabs

Compressive membrane action in axially restrained hollow core slabs: Experimental investigation

AbstractWhen a concrete slab is excessively loaded due to an accidental event, compressive membrane action can be activated in order to generate an alternative load transfer to the remaining supports, which can considerably enhance the load‐carrying capacity. This can increase the structural reliability of the components, delay or even prevent a progressive collapse and consequently increase the robustness of concrete structures. Although the beneficial effects of compressive membrane action in reinforced concrete slabs have been recognized for decades, only limited research has been focusing on this effect in prestressed concrete members, like hollow core slabs. Therefore, a novel real‐scale test set‐up has been developed in order to assess this phenomenon in real‐scale hollow core slabs. The results indicate that, despite the presence of the large hollow cores, compressive membrane action can significantly improve the load‐carrying capacity of hollow core slabs under excessive loading. In parallel, a numerical finite element model has been established in order to model the structural behavior (i.e., compressive membrane action) as per the investigated test program. The model was able to correlate the results from the experiments very well, and emphasized the large influence of the concrete tensile strength on the ultimate failure load of concrete hollow core slabs in compressive membrane action.

Experimental study of shear transfer in slim floor systems using precast concrete hollow core slabs and steel beam with web circular opening

Abstract Steel-concrete slim flooring system using precast concrete hollow core slabs and steel beam with web openings is an innovative construction system designed to combine the high bending resistance of both precast prestressed hollow core slabs and steel beam with web openings. This system can provide floor systems with a minimum constructional depth in comparison with ordinary composite floors. The aim of this study was to evaluate in an exploratory way the shear transferring mechanism between the steel beam with circular web opening and the precast hollow-concrete slab. The shear connection is formed by in-situ concrete passes through the web openings and infill the voids of the precast slabs. One push-out test was conducted to investigate the shear transferring mechanism of shear connection and the experimental results were compared to analytical methods. The shear resistance of the shear connection was predicted with good accurate by analytical methods.

Investigate the carbon footprints of three intermediate flooring systems: Cross-laminated timber, solid concrete, and hollow-core precast concrete

This paper evaluates and compares the embodied energy and embodied carbon using a Life Cycle Assessment (LCA) approach for three different intermediate floor structures, all of which use prefabricated materials-cross-laminated timber (CLT), precast hollow-core concrete, and solid concrete-to decide which floor construction materials have less environmental impact for use in the construction of a semi-detached house in the UK. The Inventory of Carbon & Energy (ICE) and the Carbon Calculator tool were used to calculate the carbon footprint from "cradle to grave" to determine whether the use of a CLT solution provides improved environmental performance over the traditional concrete solutions. The carbon footprint results indicate that the use of a hollow-core precast concrete floor system emits less carbon than the other two systems, although the concrete requires more fossil fuel input than the timber during the manufacturing process, so based on this, the footprint from cradle to gate for the timber was expected to be the less than that of the concrete. However, the results show the opposite; this is because of the differences in the material quantities needed in each system.