Precast Elements Research Articles

EXPEDITIOUS NUMERICAL CAPACITY ASSESSMENT IN PRECAST STRUCTURES VIA INELASTIC PERFORMANCE-BASED SPECTRA

The seismic design of precast structures hinges on unique characteristics intrinsic to precast technology. Emphasis is placed on lightweight structural elements for efficient on-site assembly and cost reduction. This leads to increased slenderness in beams and columns compared to traditional cast-in-situ constructions, accentuating the role of second-order effects. Dry pinned joints, favoured for connecting beams and columns, contribute to the overall efficiency in assemblage. Cast-in-situ concrete is typically reserved for connection to foundations and topping precast floor elements. Pinned joints transform the structure into an ideal isostatic system, with cantilevered columns anchored securely at the base, in designers' mind. However, this transformation reduces the energy dissipation capacity, preventing plastic hinge formation in beams and amplifying P-Delta effects in columns. The simplified approach proposed herein assesses dynamic instability in single and multi-storey precast hinged frames, providing a tool for expeditious numerical capacity assessment, useful at the initial design stage. The goal is to predict dynamic collapse and/or the attainment of specific seismic-oriented limit states based on fundamental structural parameters. Incremental nonlinear dynamic analysis, utilising far-field ground motion records, is employed to evaluate performance of a variety of precast structures modelled as equivalent single-degree-of-freedom systems. The outcomes yield inelastic spectra that provide insights into the structural capacity in terms of response modification factor and could help analysts/designers towards seismic performance-based design as well as the assessment problem. These spectra, which can themselves be taken as metrics for structural performance evaluation (in addition to as a reliable tool/means for design), are generated based on various structural parameters, including building height, column aspect ratios, and floor mass configurations, in relation to different limit states typically deemed crucial in the design of these structures for earthquake-induced actions. Regression analyses of median spectra show that polynomial expressions could fit them with good accuracy, as testified by a coefficient of determination in the 0.76-0.98 range for most of the cases.

Digital workflow to support the reuse of precast concrete and estimate the climate benefit

Abstract Concrete production contributes to around 8-9% of global CO2 emissions. Reusing building components in a circular economy can contribute to closing material loops and lowering CO2 emissions. When reusing concrete elements, it is necessary to have effective methods for evaluating their reuse potential. In this study, a novel digital workflow is developed to support the reuse of precast concrete elements by evaluating their lifespan based on carbonation depth. The workflow relies on automated retrieval of material quantities and information from a digital model. This model is then coupled with environmental data on construction products and calculation methods for CO2 uptake in concrete by carbonation. The remaining service life of concrete elements was calculated for a case study. For reference, CO2 uptake during the first service life was estimated at 4973 kg CO2 or 4% of the embodied carbon. Hence, the potential benefits of reuse outweigh those of carbonation. The presented approach supports the decision-making process when evaluating the reuse potential for concrete elements. The digital workflow can help designers make quick decisions concerning the lifespan and carbon footprint of concrete. The digital tool can be extended in future work with more parameters to evaluate additional sustainability indicators.

Optimal Location for Tower Crane and Dynamic Trailer Parking in High-Rise Modular Building Construction Project

Optimization of tower crane positioning is essential in precast building construction to ensure that a crane is in the right position to offer the best value for placing precast elements. The first goal is the optimization of transportation distances made by tower cranes, which will address the issues of efficiency and cost. This is done in a way that provides for minimization of the distances that lie between the trailer parking where elements are parked, the tower crane, and the construction installation point. However, current research fails to address the dynamic movement efficiency of trailers, especially when handling multiple trailers and several models of tower cranes, making this scenario an optimization problem that is classified as NP-hard due to the likelihood of causing a combinatorial explosion. This work endeavors to present a new mathematical model that has been applied to the Genetic Algorithm (GA). The ideal demand-generated model is designed to solve the optimal model and position of tower cranes and the prospective positioning of trailers for parking. The feasibility and applicability of the method exploited in the study are also established through a project case study. When adopting the proposed planning model compared to the earlier planning scale, comparisons highlight a small yet significant saving of 6% in time and cost when lifting elements instead of providing them from the trailers by setting up a new on-site stockyard. In addition, a great deal of enhancement is also observed in the final solution aspects, where the developed GA has even reduced the operational time and cost by half a percent each. The results of this research offer best-practice approaches to the position analysis of tower cranes in precast building construction to bring scalability and cost optimization to bear on the construction business.

Multilayer prefabrication in practice

Pre-cast reinforced concrete walls manufacturing is still associated in Poland with large-panel construction, all the advantages of which have been crossed out by technological imperfection, terrible workmanship and boring, repetitive architecture. Meanwhile, modern large-panel prefabrication provides almost unlimited creative possibilities and ensures much better quality than traditional construction. The article describes application of modern multi-layer pre-cast elements made of reinforced concrete and light-weight expanded clay concrete in construction with the incorporation of BIM technology. It presents the advantages of prefabricated construction on specific examples at various scales - from single-family houses to large residential and apartment buildings. It also presents in detail the implementation process from design, through BIM modelling, production and quality control of elements and assembly.

Novel 3D FRP system used for more effectively and readily strengthening of precast concrete elements

The burgeoning precast concrete market necessitates innovative strengthening solutions to ensure the durability and safety of precast elements. This study presents a 3D Fiber Reinforced Polymer (FRP) system designed to reinforce precast concrete elements, providing a more effective and efficient method compared to traditional Externally Bonded (EB) and Near Surface Mounted (NSM) FRP techniques. The system utilizes extended FRP strips that function as bent anchorages, U-wraps for anchorage protection, and additional FRP patches to prevent anchorage cutoff at bent corners. A comprehensive experimental campaign involving 33 specimens assessed the system's performance, demonstrating significant improvements in flexural and shear capacities with minimal surface preparation requirements. The experiments included varying strip widths and anchorage configurations to optimize the system's effectiveness. Numerical models were developed to simulate the flexural behavior of the 3D FRP reinforced elements, accurately predicting load-deflection responses and failure modes. Both experimental and numerical results suggest that the 3D FRP system not only enhances the load capacity and structural integrity of precast concrete elements but also simplifies the installation process, offering a promising solution for the construction industry. The findings also offer practical guidelines for the design and fabrication of 3D FRP reinforced concrete elements, contributing to a more sustainable and economical construction approach.

Proposal and parametric investigations of square steel tubes as post-tensioned connectors for linear-shaped precast concrete elements

Given the pivotal role of connections in the progress of the precast building industry, issues such as costs, chain collapse, and low robustness in all degrees of freedom are critical considerations. This study draws inspiration from Concrete Filled Steel Tube Elements to design and investigate using simple steel tubes as joints for precast linear-shaped elements. The study proposes and examines uncomplicated joints where two precast reinforced concrete beams are positioned within the tube. The encompassment of the beams by the tube, combined with the application of post-tensioning forces, creates a sturdy integrity between the beams, resembling a head-to-head joint. Through 48 experimental tests, various connection parameters such as beam and tube cross-section height, re-bar quantity, tube thickness, and length were systematically investigated. The experimental setup utilized a three-point bending-shear testing configuration, and the results were compared with monolithic references. The findings demonstrate that these adaptive and ductile connections rapidly exhibit a capacity similar to that of monolithic exact beams. All studied parameters exhibited their influences on the capacity of the connection; however, the primary determinant is the length of the tube. Within the discussed range, the tube length should be at least twice as long as the height of the beam. Failing to meet this criterion would prevent the complete manifestation of the desired failure mechanism.

Rapid CO2 catalytic activation of binary cementing system of CSA and Portland cement

This study presents a novel approach to activating a binary cementing system composed of calcium sulfoaluminate (CSA) cement and ordinary Portland cement (OPC) using an instant CO2 catalysis. The activation led to significant and rapid strength enhancement, with the binary cement achieving a strength of 15.42 MPa immediately after activation, all within 1 min. The rapid CO2 activation catalyzed a notable heat release, accelerating the hydration of ye'elimite to form ettringite, which is a crucial component capable of bridging gaps and imparting high initial strength. Simultaneously, the CO2 activation catalyzed the increase in sulfur concentration, which in turn, also facilitated the formation of ettringite at an early age. Subsequent strength development was attributed to belite hydration. Apart from the rapid strength gain, employing CO2 activation facilitated control over the pH value of the pore solution, thus enabling the manipulation of ettringite's crystal morphology to strategically enhance the microstructure. Samples with lower pH values exhibited needle-like ettringite formations, whereas samples with higher pH values yielded rod-like and column-like ettringite crystal structures. Comprehensive analytical investigations were analyzed using XRD, FTIR, TGA, 27Al NMR, MIP, SEM, and ICP-OES. The present study provides a new perspective on the potential application of CSA-based cement, such as precast concrete element, instant concrete product delivery, and urgent reconstruction.

Characterizing the free-vibration response of a two-span rocking bridge with free-standing columns

For accelerated bridge construction (ABC), replacing traditional emulative connections of precast elements with simpler discontinuities may lead to more resilient structures with reduced expected damages after strong seismic events. This paper comprises novel free-vibration tests of a 1:10 scale two-span rocking bridge with free-standing columns with proper geometrical and dynamic similarity. The two spans induced in the model the interaction between frames with different tributary masses, as would be expected for a realistic bridge. To excite the bridge uniformly, the experimental protocol consisted of forty-nine incremental sinusoidal ground motions that were interrupted, letting the bridge vibrate freely to rest. The results were compared with six analytical models. The results showed that the structure remained undamaged for the free-vibration tests after drifts up to 6 % and did not wobble unrestricted. The results were used to obtain the dynamic properties of the system and their variation to displacement increments. Construction imperfections induced the model to rock for all excitations, including low-intensity excitations, and to vibrate with periods different from those of theoretical equations at low displacements. This behavior was critical in the comparison between experimental results and the estimates from analytical models. These findings demonstrate that rocking bridges are a suitable system to control structural damage during seismic events despite the apparent variability of the behavior under realistic conditions. However, the design of these structures must account for the effects of construction imperfections at the rocking surface. The experimental results are openly available for download in the DesignSafe Data Depot using this DOI https://doi.org/10.17603/ds2-znfv-8t55.

Comparative life cycle assessment (LCA) of the composite prefabricated ultra-shallow slabs (PUSS) and hollow core slabs in the UK

Life cycle assessment studies of precast construction methods highlight their superiority over traditional cast-in-situ construction in reducing buildings’ environmental impacts. Among the extensively used precast structural elements, hollow core precast slabs have proven benefits with their practical implementation in flooring systems across various flooring spans and live loads. This paper presents a case study comparing the global warming potential and embodied energy impacts of a recently developed lightweight prefabricated composite flooring system (PUSS) with zinghollow core precast slabs in the UK. The analysis is based on 16 live load/flooring span scenarios, between 6 and 12m. The study examines the benefits and drawbacks of utilising different concrete types in PUSS flooring, namely normal weight concrete, lightweight aggregates concrete and geopolymer concrete. PUSS with GPC demonstrates potential savings of up to 50 % in GWP compared with hollow core slabs, while PUSS with LWC exhibits potential savings of up to 35 % in total EE compared with hollow core slabs.

Anchorage capacity of bent looped wire ropes in precast concrete wall elements for T‐ and L‐ connections

Anchorage capacity of bent looped wire ropes in precast concrete wall elements for T‐ and L‐ connections

A digital workflow for assessing lifespan, carbonation, and embodied carbon of reusing concrete in buildings

Concrete is the most used construction material, accounting for 8 % of global CO2 emissions. Various strategies aim to reduce concrete's embodied carbon, such as using supplementary cementitious materials, utilizing cleaner energy, and carbonation. However, a large potential lies in reusing concrete for new buildings in a Circular Economy, thereby closing material loops and avoiding CO2 emissions. This study focuses on the reuse of precast concrete elements. We present a digital workflow for assessing reuse by predicting the remaining service life, estimating CO2 uptake by natural carbonation, and calculating the embodied carbon savings of concrete reuse. Both carbonation rates from EN 16757 and our investigation were applied to a case study building. While EN 16757 rates suggest that most precast elements have reached the end of their service life, our assessment shows that these elements have a sufficient lifespan for reuse. Plaster and coverings significantly delay carbonation and extend service life. During the first service life following EN 16757, carbonation was 19,2 kg CO2/m3, whereas our prediction was 5,4 kg CO2/m3. Moreover, CO2 uptake during service life, including reuse, was less than 6 % of the embodied carbon. The climate benefits of reuse greatly exceeded those of carbonation. Furthermore, carbonation did not have a decisive influence when applying Cut-Off, Distributed, and End-of-Life allocations for assessing embodied carbon of re-used elements in subsequent life cycles. The digital workflow is useful in quickly assessing lifespan, carbonation, and embodied carbon of concrete. It can be leveraged as a decision-making tool when designing for reuse.

Synthetical improvement of dynamic mechanical property and toughness for precast concrete element based on optimization design of composition and curing regime

The brittleness and toughening measures of steam-cured concrete are currently less researched aspects. This study focuses on exploring the improvement in the toughness of steam-cured concrete and evaluating its influence on dynamic mechanical properties through a series of macroscopic performance tests. These tests include four-point bending tests, three-point bending fracture tests, uniaxial compression tests, and drop hammer impact tests, all conducted from the perspective of optimizing composition materials and steam curing regimes. The experimental results indicate that, under a relatively short heating time and a prolonged constant temperature curing period, the pure cement steam-cured concrete (S1 group), compared to the S2 group which used 20 % FA and 10 % GGBS to replace cement while also increasing the aggregate content with a modified steam curing regime, exhibited higher strength and elastic modulus but also showed greater brittleness. For example, the damping ratio increased to 0.6–0.7, the flexural-to-compressive strength ratio exceeded 6, and the number of specimens damaged by drop hammer impact significantly decreased, and the notch specimen exhibits lower peak load and displacement during fracture, with generally lower fracture parameter values. The fracture energy of the S2 group is 100–130 N·m-1 higher than that of the S1 group, reaching approximately 670 N·m-1, and the ductility index increased by 0.3–0.4. This research can provide technical support for the high-quality preparation of precast components using steam-cured concrete and offer a theoretical basis for reducing the brittleness of steam-cured concrete.

A Semantic Digital Twin for the Dynamic Scheduling of Industry 4.0-based Production of Precast Concrete Elements

Precast concrete construction enhances project efficiency, sustainability, and durability by leveraging a controlled production environment that ensures high-quality outputs. Still, the sequential nature of off-site production, encompassing casting, curing, and storage of the precast elements, is subject to significant uncertainties, including supply chain variability and environmental factors affecting curing times. Dynamic adjustments to the production schedule are essential for aligning with real-time changes, necessitating a robust framework for real-time data acquisition and analysis. Dynamic Scheduling (DS) is a responsive and adaptive approach that accommodates real-time changes, optimizes the production flow, and minimizes downtime or delays. However, the DS approach demands real-time data to quickly and efficiently respond to unforeseen challenges, which requires acquiring and analyzing production-relevant data throughout the production process. The Digital Twin (DT) emerges in Industry 4.0 (I4.0) as a bridge between physical operations and digital capabilities, enabling a seamless flow of information, for which the Asset Administration Shell (AAS) is a reference implementation. This study introduces a DS framework to optimize precast element production, utilizing a DT for real-time data aggregation across the production system. The framework implements a Semantic DT based on the AAS and the Linked Data approach. It employs Resource Description Framework (RDF) serialization of the AAS and an ontological representation of the production system for data integration. The framework leverages a simulation-based scheduler, which exchanges data with the DT in a Service-oriented Architecture (SoA) using SPARQL, a language for querying and updating graph databases. The approach is evaluated through a proof of concept, demonstrating effective uncertainty management in a dynamic production environment.

Full-scale tests of two-storey precast reinforced concrete shear walls: Investigation of strength and deformation capacity

Precast concrete structures behave differently than equivalent in-situ cast solutions mainly because of the narrow connections between the precast elements. In this context, the keyed shear connections are of particular interest, as they have to ensure structural integrity in order to transfer shear- and normal stresses between adjacent elements. Extensive experimental studies (based on push-off tests) of this type of connection have been conducted in the past. These tests typically showed significant softening in the post-peak regime of the shear-slip relationship. It is for this reason important to study how effectively such connections can be utilised on the level of structural systems, where redistribution of internal forces is often required to reach the global load carrying capacity. This paper presents results from full-scale testing of two precast shear wall structures. The structures were two stories high and simulated a typical segment of precast buildings in practice. Each test structure was composed of 12 precast elements (decks and walls) and tested to failure under a combination of vertical and horizontal loads. The main varying parameter between the two tests is the design shear capacity of the keyed connections, which was doubled from test T2 to test T3 by increasing the diameter and the yield strength of the U-bar loops. Both structures displayed a ductile failure with significant deformation capacity. However, despite the higher strength in the keyed connections, the load carrying capacity of test T3 was not increased compared to test T2. This behaviour can be explained by a comprehensive analysis of the measured deformation field obtained from 2D Digital Image Correlation. By comparing the deformations with information obtained from independent component push-off tests with equivalent connections, it is possible to pinpoint the different stress regimes that the critical connection experienced, when the test structure reached its load carrying capacity. The results show that at that point in time, large parts of the critical connection were still in the pre-peak shear-slip regime, while another part located between two window openings was already at the end of the post-peak regime with practically no residual strength left. The findings indicate that the effective design strength of connections should be chosen with caution when modern numerical rigid-plastic methods are used to calculate the load carrying capacity of precast structural systems.

Renovation with height increasing of residential buildings of the 1960s made of precast concrete

For many years, an urgent problemin Ukraine is a technical renovation of the existing housing stock of mass-series buildings. Most of them were built with precast concrete elements inthe 1960s–1970s. The design lifecycle of such buildings was determined for 25 years. Therefore they have obsolescence and backwardness. That expressed in inconformity with modern design codes for residential buildings, the absence of elevators, the unavailability of engineering communications, low heat and energy efficiency and environmental compatibility of such buildings. On the other hand, the technical examinations of concrete structures of such houses showed that at least 80 % of them havenot depleted their bearing capacity resource. The problem of buildings renovation was especially emphasized by the destructive consequences of theRussian federation armed aggression in Ukraine. The paper describes the experience of renovation with reconstruction of the old 5-storey residential building into modern 9-storey multi-apartment residential building. Construction works included redevelopment of the interior space, elevator installation, and replacement of the utilities by the modern ones and using of up-to-date technologies to improve the energy efficiency of the building. The project provides increasing the number of stories.

Synchronizing production of precast elements with on-site erection

Offsite construction technologies are developed to reduce project cost and duration. To make the most of the potential offered by prefabrication the planner should consider the whole supply chain. A failure to coordinate the off-site production with on-site erection is a source of waste (waiting time of the construction crews or redundant handling activities on-site). Most of the research to date focused on optimizing operations of a prefabrication plant assuming a deterministic schedule of demand for its products. The purpose of this paper is to develop a mathematical model for integrated scheduling of offsite and on-site operations. Its solution is a schedule that minimizes the downtime of both the prefabrication plant and the on-site erection crews. In accordance with the Just-in-Time concept, the prefabrication schedule is set in a way to reduce the stocks of finished products, thus reducing the storage area and cost of funds tied up in inventory. The schedule’s robustness against the disturbance in the production and erection workflows is assumed to be assured allocating time buffers. The advantage of the proposed method is the ease of collecting the input: instead of detailed cost records, estimates of unit cost of lost time can be used.

Fastening in concrete vs. rock mass—Comparative determination of pull‐out loads for artificially created discontinuities in concrete

AbstractPossible discontinuities in the subsurface have a major impact on the load‐bearing behavior of post‐installed fastenings. For concrete, the behavior of post‐installed anchors and thus their design can be clearly addressed as concrete is assumed as a homogeneous fastening substrate. This is valid except, for example, in the area of building joints and at joints of precast concrete elements, where the formation of structural joints inevitably occurs and which basically correspond to a separation surface. In contrast, rock mass is characterized by the rock type, but is generally also significantly influenced by its discontinuities. These play a decisive role concerning rock mass stability and show a great impact on the load‐bearing capacity of rock, especially for fasteners with a shallow embedment depth. It is to be assumed that the same also applies to separating surfaces in concrete. Furthermore, the question arises as to the non‐destructive preliminary detectability of such weak zones. For carrying out a comparative study under controlled conditions, artificial interfaces of different geometries were generated in concrete in laboratory tests by inserting PTFE layers at different positions of the test member. Pull‐out tests of post‐installed fastening systems were carried out in their vicinity to determine the load transfer as well as the failure mode. It could be shown that discontinuities have a negative effect on pull‐out loads not only in the rock mass, but also in concrete. However, detection of these by means of a rebound hammer was only possible in the rock mass.

Experimental investigation of dowel action in reinforcing bars using refined measurements

AbstractIn typical reinforced concrete design, reinforcement is designed to carry axial forces, but it can also resist transversal forces by dowel action. This is usually neglected for simplicity's sake in the design phase, but it can be accounted for either explicitly in mechanical models or implicitly in empirical relationships. Furthermore, there are cases where the connection between various concrete elements explicitly depends on dowel action, as for example, in connections between precast elements or between two concrete parts cast at different times. On the other side, dowel action can have a negative impact on the fatigue resistance of reinforcing bars subjected to cyclic loading, because of the local stress concentrations near interfaces due to relative movements, either in sliding or in opening of cracks not perpendicular to the bar. For the assessment of the remaining capacity of existing structures, improved models of the behavior are needed, including realistic models of the behavior of concrete, steel and their interfaces. The aim of the present paper is to provide a contribution to a better understanding of dowel action by two test series. The first series focused on the behavior of the dowel: the concrete specimens with the embedded bars were placed in a custom‐made test setup and subjected to monotonic or low stress‐level cyclic actions with a longitudinal and a transversal crack opening component, up to developing the full plastic capacity of the dowel and rupture at the peak of catenary action. The measurement system included tracking the displacement field at the surface of the concrete and the strains in the dowel by optical fibers glued on its surface. The latter measurements allow to derive the internal forces in the reinforcing bar and deformed shape of the bar as well as the contact pressure between the bar and the surrounding concrete. The results show a strong dependency on the test variables: diameter of the bar, imposed crack kinematics and angle between the bar and the crack. The second test series looked more closely at the behavior of concrete underneath the bar, in the presence of a point load introduced at various locations into concrete through a reinforcing bar. A comparison of the test results with existing models shows a general good agreement and some aspects that deserve to be improved.

Structural behavior of jointed precast concrete beams reinforced with GFRP bars

This experimental research aims to reduce the joint length between the precast concrete elements reinforced with GFRP bars. The experimental work was divided into two stages. Stage (I) consists of twelve specimens made from GFRP bars and jointed together using GFRP or steel sleeves filled with epoxy resin. The specimens were tested under tension up to failure to investigate the tensile capacity of splice bars taking into consideration different parameters such as sleeve type, embedment length, bar size, and sleeve radial stiffness. While Stage (II) consists of ten reinforced concrete beams measuring 200 × 350 × 3300 mm. All beams were tested under a four-point bending load up to failure. The connection types for GFRP bars were investigated using two methods; (i) the optimum sleeve connector selected from stage I, (ii) using lap splice with different parameters such as splice length, joint compressive strength, and confinement lap-splice region with GFRP sheets. The test results show that an adequate bar embedment length and sleeve radial stiffness are required to achieve bar tensile strength. Whereas lap splice length can be reduced by increasing confinement of lap splice region with GFRP sheets. Finally, precast elements' joint length can be minimized by using a sleeve connector with adequate radial stiffness and embedment length equal to 15-times bar diameter or by confinement of the lap splice region to minimize its length to 40-times bar diameter.

Calculation of prestressing force losses in precast elements interconnected with concrete topping

Calculation of prestressing force losses in precast elements interconnected with concrete topping