Post-tensioned Slabs Research Articles

Application of steel fiber reinforced-concrete in post-tensioned flat slabs: A numerical study

Despite the outstanding mechanical properties, SFRC is still underutilized in the load-bearing structures, mainly being restrained to the non-structural applications. This paper primarily investigates the effect of the innovative combination of steel fibers and the post-tensioning on the performance of concrete slabs and assesses the feasibility of using steel fiber as substitute for the conventional reinforcement in post-tensioned slabs. Building on the experimental work done by Virginia Polytechnic Institute and State University, numerical and theoretical analyses were employed to verify and extend the experimental findings. In the paper, two different reinforcement solutions (steel fibers or conventional reinforcement) were used in the slabs, and they were combined with four different tendon layouts. Among them, the banded-banded tendon coupled with steel fibers significantly enhanced the punching shear resistance of the slabs. To deepen the understanding of SFRC’s viability as a structural material, the flexural strength of the slabs obtained from nonlinear finite element analysis (NLFEA) is compared against the theoretical results of design methods outlined in fib Model Code 2010 (MC2010), new FprEC2:2022 (prEN 1992–1-1:2022(E)), IAPMO UES ER-465 (IAPMO 465), and Norwegian NB 38 (NB 38). The results indicates that some of the certain provisions in the American and European Codes might be simplified, for instance: 1) steel fibers might be used as the only reinforcement to replace the minimum required bar reinforcement in post-tensioned slabs, and 2) combination of steel fibers and banded tendon layout, which could further simplify the construction process, might be applied in the engineering construction.

Punching shear behavior of flat slabs with post-tensioning in one direction

Post-tensioned flat slab (PT) system has become widely used in the construction field in the recent time. The main advantages of the post-tensioned slab system are strength improvement and resource savings. Additionally, the conventional post-tension flat slab is an economical system, especially for long-span structures. However, it may not be suitable for structures with significant variations in spans in both directions of the slab. The unidirectional post-tensioned slab, which involves a post-tensioning system in one direction of the slab and a normal reinforced concrete flat slab system in the perpendicular direction. This offers an effective solution for the specific issues mentioned above. This system is also recommended for structures with expansion joints that do not have enough space to install the post-tension system and tensioning machine. In the current research, the punching shear behavior of conventional bidirectional PT slab was compared to unidirectional PT slab counterparts. Five post-tensioned specimens were tested to investigate the punching shear behavior for unidirectional PT slabs at different parameters. Variation of precompression stress level using different numbers of tendons and distribution of tendons were the variable parameters studied in unidirectional PT slabs. All slabs were exposed to static loading until failure using a 2200 kN hydraulic jack with a pump capacity. Deflection behavior of all slabs was measured using a linear variable differential transformer device (LVDT). Additionally, strain gauges were fixed on concrete, steel bars, and tendons to evaluate the strain of each item. The results obtained that the five tendons unidirectional PT specimens had a 1.4% reduction of punching shear resistance compared to bidirectional PT specimen counterparts. Increasing precompression stress improved punching shear capacity. Specimens with banding tendons at the punching shear zone enhanced punching shear capacity by 4.5% more than those with distributed tendons. The study also indicated that the ultimate punching shear failure load was the highest in conventional post-tensioned specimen. Additionally, the unidirectional post-tensioned slabs with five tendons and a precompression stress of around 1.5 MPa exhibited a 1.2% slightly higher ultimate failure load than the unidirectional counterpart with seven tendons and a precompression stress of around 2.5 MPa, However the seven tendons specimen had the best deflection behavior compared to all specimens. The three tendons specimen with a precompression stress around 1 MPa, the lowest precompression stress, exhibited the lowest ultimate failure load. The calculated punching shear capacities of all specimens from conventional post-tensioned flat slabs equations of various codes, such as the American Building Code (ACI-214), Euro Code (EC) and Egyptian Practice Code ECP-203, are compared to the existing experimental results. For the studied specimens, the cost of unidirectional PT slabs was more economical by around 29% compared to a conventional PT slab.

Structural Response of Post-Tensioned Slabs Reinforced with Forta-Ferro and Conventional Shear Reinforcement under Impact Load

Structural Response of Post-Tensioned Slabs Reinforced with Forta-Ferro and Conventional Shear Reinforcement under Impact Load

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.

An automated optimized design of practical post-tensioned slabs

In this paper, an efficient methodology that could be implemented within any analysis software is developed to automate the design process of post-tensioned slabs. Optimization techniques are used to compute the necessary number of strands. The present methodology is based on computing an innovative influence matrix that contains the effect of each strand on stresses at a set of control points (points of peak stresses). This matrix will be used in the optimization avoiding reanalysis in each optimization iteration. The sum of the squares of the difference between the allowable stress and the computed stresses at all control points is considered an objective function. The optimization is then carried out under the constraints that the stresses at each control point should not exceed the allowable limit and to ensure that the number of strands is an integer value. Alternatively, the proposed methodology could be used as a value-engineering tool. Practical examples are presented to demonstrate the efficiency of the developed methodology.

Investigating the Behaviour and Strength of Unbonded Pre-tensioned RC Slabs Subject to Flexural Loads

Unbonded pre-tensioned systems, in which tendons are greased and wrapped in plastic sheathing, have several benefits in comparison to bonded systems. However, analytical evaluation of their capacity is taxing due to the iterative compatibility conditions necessary to determine the system’s behavior using the empirical equations available in the literature. To investigate the behaviour and strength of unbonded pre-tensioned RC slabs subject to flexural loads, four simply-supported post-tensioned slabs with unbonded tendons were tested in flexure. Experimental failure loads and tendon strains were compared to the ACI 318-19 provisions. While the provisions for unbonded specimens were found to be accurate, the strain in the unbonded tendons exceeded the yield stress in all specimens, suggesting that ACI 318-19’s stress limitations on unbonded post-tensioned concrete are unwarranted. The unbonded system also showed better crack control at the failure stage when non-prestressing steel reinforcement is used when compared to system with no non-prestressing steel.

Sustainable concrete structures by optimising structural and concrete mix design

ABSTRACT Sustainable concrete construction can be achieved by combining optimised structural designs with low-carbon concrete (LCC). This paper demonstrates the importance of sustainable construction by analysing various design options for a typical suspended slab system in high-rise buildings. Pearson (2020) noted that concrete slabs make up approximately 47% of the embodied carbon (EC) in commercial and residential structures, with slabs alone comprising around 70% of the total concrete volume in residential buildings. This presents an opportunity to reduce EC through structural design choices. The analysis in this paper involved designing a post-tensioned (PT) flat slab system for a residential development in Sydney and then re-designing it as a reinforced concrete (RC) slab by adjusting slab thickness and reinforcement system. A key finding was that transitioning from an RC to a PT slab resulted in a 44% total EC reduction when using a 100% General Purpose Cement (GPC) blend. Further EC reductions can be achieved by implementing LCC. The chosen LCC blend for this study is 23% Fly Ash, 23% Ground Granulated Blast Furnace Slag, and 54% Cement (FA/GGBFS/GPC), demonstrating a 36% reduction in EC compared to a 100% GPC blend while maintaining acceptable workability, constructability, mechanical, and durability properties.

Experimental and numerical investigation of punching and post-punching shear capacities of post-tensioned flat plate slab-column joints influenced by prestressing levels

Post-tensioned slab systems serve as an effective method to enhance the progressive collapse resistance of concrete flat plate structures by significantly improving the punching shear and post-punching capacities of their slab-column joints. While the existing research mainly focused on the punching shear behaviour of post-tensioned slab-column joints in small deformation stages, the post-punching behaviour in large deformations has been overlooked. This study aims to fill this research gap thorough experimental and numerical studies. Experimentally, four slab-column joints, including three post-tensioned specimens (with varied prestressing levels) and one specimen without tendons, were designed and tested. Detailed failure process and load-resisting mechanisms of the specimens at different deformation stages were discussed. The test results confirmed the efficiency of post-tensioning in improving the punching shear performance. Varying prestressing levels have influenced the development of punching shear capacity but did not affect the growth rate of load resistance in the initial post-punching stage. Numerically, validated finite element models were used to predict the post-punching capacities of the specimens. The numerical results indicated that post-tensioning helped increase post-punching capacities, but such an enhancement was independent of the prestressing levels. Additionally, the influence of the rupture strains of both tendons and reinforcement on the post-punching capacity was investigated through a parametric study.

Acoustic emission technology-based waveguide localization method for damaged internal tendons of in-service post-tensioned hollow slab bridges

Prestressing tendons are crucial load-bearing elements in post-tensioned hollow slab bridges. Damage to these tendons significantly reduces the safety, functionality, and longevity of the bridge. Regular monitoring of prestressing tendons is essential for bridge operation. Acoustic emission technology, known for its high accuracy and sensitivity to minor vibrations, is a key technique for monitoring bridge cables. This study proposes a novel dual-sensor acoustic emission localization method for detecting tendon damage in post-tensioned hollow slab bridges, utilizing waveguide technology. The effectiveness of this method is confirmed through hammering tests that simulate acoustic emission damage on operational hollow slab bridges. The proposed method, requiring only two sensors, offers a cost-effective alternative for monitoring the entire span of post-tensioned hollow slab bridges, so that effectively reduces the cost of bridge health monitoring and is easy to be promoted in actual engineering projects.

Machine learning base models to predict the punching shear capacity of posttensioned UHPC flat slabs

The aim of this research is to present correction factors for the punching shear formulas of ACI-318 and EC2 design codes to adopt the punching capacity of post tensioned ultra-high-performance concrete (PT-UHPC) flat slabs. To achieve that goal, the results of previously tested PT-UHPC flat slabs were used to validate the developed finite element method (FEM) model in terms of punching shear capacity. Then, a parametric study was conducted using the validated FEM to generate two databases, each database included concrete compressive strength, strands layout, shear reinforcement capacity and the aspect ratio of the column besides the correction factor (the ratio between the FEM punching capacity and the design code punching capacity). The first considered design code in the first database was ACI-318 and in the second database was EC2. Finally, there different “Machine Learning” (ML) techniques manly “Genetic programming” (GP), “Artificial Neural Network” (ANN) and “Evolutionary Polynomial Regression” (EPR) were applied on the two generated databases to predict the correction factors as functions of the considered parameters. The results of the study indicated that all the developed (ML) models showed almost the same level of accuracy in terms of the punching ultimate load (about 96%) and the ACI-318 correction factor depends mainly on the concrete compressive strength and aspect ratio of the column, while the EC2 correction factor depends mainly on the concrete compressive strength and the shear reinforcement capacity.

The examination of the slabs formed with hollow plastic modules

There are various slab systems in reinforced concrete buildings, and these are slabs settling on beams or shear walls and operating in one or two ways, one- or two-way ribbed (cassette) slabs, t-beam slabs, mushroom slabs, and pre-tensioned or post-tensioned slabs. Apart from these, the hollow core slabs are of distinct importance. Among these slabs that settle on the ground, there are ones with hollow cores and also ones with closed-cells. Such slabs are able to protect human health against the negative effects of water, moisture, and ground gases. In this study, the difference between Cobiax slabs (bubble deck slabs) and hollow core slabs settling on the ground was revealed. The principle of the systems in question is pouring of concrete on open-cell or closed-cell voided plastic components in the slab. Both in the open-cell module slab systems or in closed-cell module systems concreted by placing plates on them, advantages such as prevention of moisture through ground ventilation, reduction of building’s load, contribution to sound and heat insulation, and release to atmosphere of radon ground gases, which are hazardous on human health, are ensured.

Comparative analysis of RCC and PT Slabs underneath Lateral Loading: A Structural study using ETABS

ETABS software is used to analyze the structural response of reinforced concrete (RCC) and post-tensioned (PT) slabs under lateral loading. This study investigates RCC and PT slabs’ behavior by using finite element analysis to determine bending moments, shear forces, and storey drift. Prestrassed slabs display lower bending moments and shear forces than RCC slabs, demonstrating the effectiveness of prestressing in reducing structural requirements. A reduction in storey drift also indicates improved resistance to lateral deformations in PT slabs. In terms of structural performance and cost-effectiveness, PT slabs offer potential benefits for constructing layouts and construction, making them an attractive choice.

Geotechnical Properties of Residual Diyarbakir Basaltic Clay in Turkey

Diyarbakir province mean rock formation is basaltic due to its location. Basaltic parent rocks release much silt or clay when imposed to chemical or physical weathering. The soils are residual in origin. In other words, they formed in situ where the basaltic parent rocks exist. They were not transported by means of wind or water. In this research, firstly, the properties of Diyarbakir basaltic clays were investigated from literature. After that, one soil sample from Kayapinar vicinity has been taken to laboratory to find index properties. The values from two different locations which are obtained from literature and values which are obtained from laboratory were compared. The results indicated that the three samples from different locations showed roughly the same index properties. As per the results, the clay is high plastic (CH), and it has swelling potential. In this thesis, design parameters of posttensioned slabs on ground under different climatic scenarios were found. The widely used method for slabs on ground under swelling soils is the Post‐Tensioning Institute (PTI) method. In order to use this method, Thornthwaite moisture index is required. This index is used in geotechnical engineering to identify moisture flux boundary conditions for unsaturated soils and depth of active zone for expansive soils. This index has been found using water balance sheet tables for Diyarbakir. So as to find the future moisture index, water balance sheet tables have been formed finding the climate projection data for Turkey in literature. In this way, five moisture index values of Diyarbakir have been found for the current situation and with regard to representative concentration pathway (RCP4.5 and RCP8.5) scenarios for 2050. The parameters for the maximum differential swell (em) and the angular moisture change index (ym) for design procedure according to the PTI method were found for each moisture index. Results showed that the ym and em values increased when the Thornthwaite moisture index is reduced. Also results showed that the slab thickness is increased when moisture index is reduced. Considering the moisture index parameters for future values, Diyarbakir is likely to face arid climates in the future.

Experimental work of effect of openings on the post-tensioned flat slab

This study aims to evaluate the effect of various parameters on the behavior of the reinforced concrete flat slabs and the contribution of each design element in the punching shear strength. This research presents experimental results of tested post-tensioned flat slabs with opening under concentric compressive load. The developed post-tensioned flat slabs are to ensure adequate punching shear strength capacity. The experimental work consisted of eight specimens of post-tensioned reinforced concrete flat slabs which classified into groups. All slabs had the same dimension and reinforcement. The slabs had dimensions with a 1750 mm length and 1750 mm width, to study the behavior of post-tensioned flat slab with/out openings under the concentrated load and punching influence.

Structural Behavior Comparison on Earthquake Resistance of High-Rise Mall Building (Framed Structure,Flat Slab and PT Flat slab)

The rate of urban population growth and the amount of available space had a significant impact on the construction of high-rise mall buildings in developing countries like the USA, UK, Australia, and Hong Kong. These high-rise mall constructions may be constructed using a variety of structural techniques. Today, RC Frame structures are often employed in constructing. Usually, these structures are employed to counteract the sizeable moments brought on by applied stresses. On the other hand, flat slab structural systems, in which the slab is directly supported by columns, have lately been adopted in many buildings because they have the advantage of greater clear floor-to-floor heights to satisfy the economical, easier form-work, quicker construction duration, and architectural needs. On the other hand, with a post-tensioned slab, the PT flat slab Structural System uses high-strength tensioned steel strands to compress the slab, maintaining the bulk of the concrete in compression. When compared to RC framed structural system, this results in a very efficient construction that minimizes partial consumption and reduces the economic span range. Three cellar+Ground+9 higher floors structural models of a high rise mall building with RC framed structure, flat slab, and PT flat slab structural system arrangement are taken into consideration in the current study. The study is completed by taking into account seismic zone II and type I soil condition, and it takes into consideration the susceptibility of purely RC framed structures, solely flat slab, and completely PT flat slab systems. The structural behavior of an RC-framed structure, a flat slab, and a PT flat slab are being compared for earthquake loads. The response spectrum approach is used to do the analysis.With the use of analytical tools, parameters such as storey displacement, storey drift, base shear, and storey shear are calculated. The findings are then compared between three structural system.

Cutting On Existing Bonded Post-Tensioned Slabs: Safety Precautions, Procedures and Execution

Post-formed cut-off or cutting of the post-tensioned slabs is a common practice during post-tensioning work. However, cutting on existing post-tensioned slabs must be done carefully to avoid severe damage to the building. The measurements during the design review are critical in considerations of post-cutting conditions, variations between shop drawings and site, possible grouting failure and excessive deformation. This paper presents a successfully execution of cutting operations on bonded post-tensioned slabs without compromising the structural strength and serviceability. There are procedures and requirements that need to be considered prior to cutting at the design stage, prior to cutting at the site and at slab cutting stage. The safety precautions are necessary for unintentional scenarios that require immediate action. Cutting the slab creates potential hazards. It was found that the grouting material plays an important role not only in solidifying the concrete but also in forming a secondary anchorage mechanism. Therefore, selection of suitable grouting material should be based on the dimension of the locking area. In contrast to unbonded post-tensioned slabs, bonded post-tensioned slabs do not require de-tensioning and re-tensioning.

Comparison of the post-tensioned, solid, hollow block, and flat slabs in terms of economy considering different span lengths

From among the several types of slabs, there is uncertainty about the most cost-effective one for structures with short, medium, and long spans. A study comparing the cost of the solid, flat, hollow block (HB), and post-tensioned (PT) slabs for 4, 6, and 8m spans was conducted using SAFE software. For each span length, the total quantities of concrete and steel bars were found and compared for 4 slabs. Then, the total cost of steel bars, concrete, blocks, tendons, and formwork was tabulated and compared. The findings revealed that the quantity of concrete in slabs with 4 and 6m spans is the least in the HB slabs, while for slabs with 8m spans, the quantity of concrete is the least in the PT slab. Besides, the quantity of steel bars in slabs with 4, 6, and 8 spans is the least in PT slabs. In terms of economy, the most cost-effective option is the flat slab for 4m spans, with savings of about 14, 9, and 17% compared to solid, HB, and PT slabs, respectively. On the other hand, for 6 and 8m spans, the most cost-effective option is the PT slab, with savings of about 10, 6, and 6% for the 6m span, and 10, 20, and 22% for 8m span compared to solid, HB, and flat slabs, respectively. Therefore, for 6m spans and more, PT slabs offer significant cost savings.

Differential Study of Reinforced Cement Concrete Slab and Post-tensioned Slab

Differential Study of Reinforced Cement Concrete Slab and Post-tensioned Slab

The Use of De-Icing Salts in Post-Tensioned Concrete Slabs and Their Effects on the Life of the Structure

This article expounds on the problem of the use of de-icing salts in the corrosion of steel rebars in bridge decks and their effect on post-tensioning elements. In particular, this paper focuses this problem on structures affected by an aggregate–alkali reaction and without any waterproof treatment using the example of one structure whose repair was carried out in 2020. In this structure, the internal stresses due to the aggregate–alkali reaction caused longitudinal cracks in the upper face of the deck, through which the penetration of chloride ions was concentrated, causing, finally, the brittle fracture of the steel bars and the corrosion of the prestressing elements. This article also explains some conclusions about the most probable mechanisms that resulted in the brittle fracture of the steel bars due to the extraordinary and unexpected nature of this phenomenon.

Parametric Study of Drilling Method Performed on One-Way Post-Tensioned Slabs

Abstract Determination of the stress state in concrete structures is a very important, but difficult task. In the case of new structures, it is possible to easily instal measurement instruments which can provide important data as a part of real-time monitoring. However, the evaluation of stresses in existing structures is much more challenging. Currently, stress relief methods are a well-established approach for the evaluation of the actual state of existing structures. The so-called Drilling method (also known as Stress-relief coring technique) is one of the possible techniques for such analysis. For practical use of this method, knowledge of pivotal factors which influence stress relief is crucial. Therefore, this paper presents a parametric study performed on a one-way post-tensioned slab which can help to understand the effect of the depth of the core and the distance from the edge of the hole (position of strain gauges) on the change in stress in the vicinity of the drilled core. Finally, based on the obtained data, the recommendations for the subsequent experimental program will be summarized. According to the study, it seems that the depth of drilled core does not significantly influence the stress relief and the main impact can be attributed to distance from the edge of the hole.