Permanent Formwork Research Articles

Experimental study on interior precast concrete beam-column connections with UHPC core shells

High-performance materials are increasingly being used in precast connections to improve their mechanical performance and simplify the construction process. In this study, a novel precast beam-column connection with an ultrahigh-performance concrete (UHPC) core shell is proposed, which works as the permanent joint formwork in the precast stage and the strengthening overlay during normal service. To investigate the seismic performance of the proposed connection, a total of three precast specimens and one reference monolithic specimen were tested through the quasi-static method. The main variables in this study were the thickness of the UHPC shell and the layout and ratio of stirrups in the joint zone. The test results indicated that the UHPC core shells effectively limited the shear behavior, delayed cracking in the joint zone, and provided plump hysteretic performance. With the assembly configuration, the proposed connection had good ductility and an efficient energy dissipation capacity. The UHPC shell configurations with variable stirrup layouts and ratios led to different crack patterns in the joint core zone. In addition, strengthened by the UHPC shells, the joint cores could be reinforced with fewer stirrups than demanded by code.

Experimental study on the flexural behavior of cold-formed U-shaped steel-encased confined prestressed RC beam

This paper discusses the flexural behavior of a cold-formed U-shaped steel-encased confined prestressed RC beam (CUSCPC). In this system, the U-shaped thin-walled steel girder provides the restraining stress to the partially confined concrete beams, participates the deformation of the composite beam under servicing loads and serves as a permanent formwork for the prestressed concrete (PC) beam during construction. Shear studs are welded on the inside of the closed end of U-shaped steel girder to provide a full shear connection between the concrete and thin-walled steel plate. Same number of CUSCPC specimen but with no shear studs were made for comparison purposes. Two additional parameters were also considered: ratio of tension reinforcement and ratio of P/S strands. The test results show that all specimens have excellent ductility and display a flexural failure pattern. The brittle behavior disappears due to the triaxial stress state of the partially confined concrete beam encased with the U-shaped thin-walled steel girder. It is also found that the load-bearing capacity of the CUSCPC beams with shear studs is increased by 5–10%, compared with the conventional PC members and the CUSCPC beams with no shear studs.

Verification Test of Restoration Effect of Offshore Concrete Structure Using Permanent Formwork Panels and Underwater Inseparable Mortar

In recent years, the deterioration of harbor structures has become a matter for concern, and the establishment of effective repair methods has become urgent. In this study, a repair method for installing permanent formwork panels and filling them with underwater inseparable mortar is proposed as an effective section-restoring method for deteriorated concrete caisson sidewalls. To investigate the integrity between existing concrete and repaired parts as well as the effect of thickness increase due to panel installation, static bending tests of a flat-reinforced concrete (RC)-beam-modeled side wall used in caisson structures are conducted. The results obtained from this study are as follows: (1) by attaching the permanent formwork panels to the flat RC beam, the bending crack occurring load was improved by a factor of three, and the rebar yielding load and maximum load were doubled. This tendency was the same even when the RC beam had a cross-sectional defect. (2) The RC beam with the permanent formwork panels finally failed with diagonal cracks opening after the maximum load was reached. The ductility ratio at this time was approximately 6. To improve the deformation performance, it is necessary to apply shear reinforcement. (3) The analysis results by the fiber model assuming the complete adhesion of the permanent formwork panels, underwater inseparable mortar, and RC beam were performed, and the results were compared with the experimental results. As a result, it was clarified that the adhesion of each constituent material was retained until the yield of the main reinforcing bar. After that, pulling out of the main reinforcing bar from the concrete and damage to the permanent formwork panel became apparent. (4) The curvature of the cross-section at the yield of the main reinforcing bar was φyc = 0.007 m−1, and it was confirmed that the assumption of plane conservation was valid in the cross-section with a curvature less than that. This research is expected to promote the efficient maintenance of existing concrete caisson structures. As the amount of cement used and the construction period can be reduced, it is assumed that the environmental load can be reduced as well.

Research on the bonding performance of TRC permanent formwork and cast-in-place concrete

The performance of the interface bond between the TRC permanent formwork and cast-in-place concrete is a key factor that determines whether the formwork can exert sufficient mechanical properties to replace traditional formwork. Sufficient performance of the TRC permanent formwork can further promote its application in engineering practice. This paper presents the results of a three-point bending test performed on a TRC formwork superimposed plain concrete beam with prefabricated cracks. The influences of various interface treatment methods, interface agent types, TRC formwork thicknesses, chopped fibre contents, textile distribution rates and other factors on the bonding performance of the interface between the TRC permanent formwork and cast-in-place concrete are considered. The study found that regardless of whether the interface is processed, the interface bonding performance between the TRC permanent formwork and the cast-in-place concrete is better than that between traditional formwork and cast-in-place concrete. After the interface is processed, the ultimate bearing capacities of the composite beam specimens are improved to varying degrees, and the crack development mode is improved. Treating the interface, increasing the thickness of the TRC formwork, increasing the formwork distribution textile rate, adding chopped fibres and other treatment methods can reduce the strain of the interface between the TRC formwork and cast-in-place concrete.

Application of a combined precast and in-situ-cast construction method for large-span underground vaults

Exploitation of large underground space calls for innovative structures and construction methods. In this paper, a combined precast and in-situ-cast method for construction of large-span underground vaults is proposed. It was applied to an engineering example in the form of the vault of the Wuzhong Road Metro Station in Shanghai. This vault consists of 56 elements. Construction of an element involves the following steps. Firstly, upper ribbed arch segments are precast in a factory. After hardening, they are transported to the site and then assembled to three-hinged arches. The latter serve as a permanent formwork. Then, steel cages are made, followed by in-situ casting of concrete. As the concrete hardens, an integral arch, representing an element of the vault, is obtained. It carries the dead load of the covering soil and the overload on top of it. Structural analysis of this example is based on transfer relations, representing analytical solutions of the linear theory of slender circular arches. From the viewpoint of engineering practice and computational analysis, the advantages of the combined precast and in-situ-cast method over the in-situ-cast method are as follows: (i) the construction period is shortened by 50%, (ii) a fair-faced concrete surface of the vault is produced, rendering decoration work superfluous, and (iii) the maximum bending moment of an element of the studied vault is reduced by 40%.

An Investigation on FRP-Stay-in-Place Concrete Composite System for Sustainable Construction

In fiber-reinforced polymer-stay-in-place (FRP-SIP) system, the FRP is structurally integrated with concrete to use as a permanent formwork that also provides tensile reinforcement to the member. The present work investigated, experimentally and numerically, the complex behavior of FRP-SIP composite system with a commercially available pultruded glass FRP section as permanent formwork. Beam and slab specimens were prepared in the laboratory with the glass FRP as permanent formwork. Flexure tests were carried out in order to understand the influence of FRP as a stay-in-place member on the load–displacement response and failure modes of the system. It was observed that the beams under flexural loading had improved flexural capacity due to FRP-SIP and failed predominantly in shear mode. Along with shear failure, delamination of the FRP was also observed in some cases. The results revealed that FRP-SIP system was capable of providing adequate flexural reinforcements to the concrete structural members and thus showed the ability of replacing steel reinforcements. A three-dimensional finite element (FE) model was developed for the FRP-SIP concrete, which was capable of capturing the multifaceted behavior of the composite system. The FE model was validated with the experimental results of the present work and also with that obtained from the literature.

Performance of expanded polystyrene light weight self compacting concrete in composite slab

ABSTRACT Composite constructions have gained importance due to faster and economical construction. Composite sections are generally made with cold formed corrugated profile sheet, which also act as a permanent formwork. To promote the use of composite sections in construction industry, it is necessitate to target to minimize the self-weight. It also facilitates to save the construction cost. In composite slabs, shear connectors are provided for composite action. It would be difficult to pour the conventional concrete; hence self compacting concrete would be ideally suited for such places. To reach the above objective, an effort has been made to investigate the expanded polystyrene light weight self compacting concrete in composite slab. To achieve the light weight concrete, expanded polystyrene beads were added in different proportions to the coarse aggregate. The composite slab was performed for four-point bending test under flexure and push out test. The test result concluded that the light weight expanded polystyrene self compacting concrete composite slab exhibit a higher performance with reduction in the thickness of the slab. The minimum spacing of shear connector was well performed. It could able to control the shear crack and de-bonding effect between the profiled steel sheet and concrete.

The influence of the bonding length on the failure mechanism of the interface between the TRC permanent formwork and cast-in-place concrete

TRC permanent formwork is made of a new type of cement-based material and has wide application prospects in formwork engineering. To promote the large-scale development of TRC permanent formwork and make it widely used in engineering practice, based on the single-lap shear test, this paper analyses the bonding properties between the TRC permanent formwork and cast-in-place concrete at different lengths in terms of the failure mode, load-slip curve, etc., and further elaborates on the fracture mechanics theory. The research shows that when the length of the formwork small, the failure mode of the specimen measured by the single-lap shear test mainly occurs at the textile-matrix interface in the TRC permanent formwork; when the length of the TRC formwork large, the failure mode begins to change to textile fracture. The effective bonding length of the TRC permanent formwork and the cast-in-place concrete is approximately 150 mm. When the TRC formwork length is less than 150 mm, the interface bonding force increases continuously with increasing TRC formwork length. The load-slip is mainly divided into two curves with typical characteristics. The first type of curve has a clear load softening stage, and the whole curve of the second type has a stage where the slip increment is small and the load drops sharply. Finally, the interface fracture energy can better characterize the interfacial bonding properties between TRC permanent formwork and cast-in-place concrete.

Time-dependent flexural performance and design procedures for steel-bars truss slabs

Thin-walled steel decks have been generally treated as permanent formwork in the routine design of steel-bars truss slabs, and their effects on the time-dependent behaviour of steel-bars truss slabs have not been quantified. The objective of this study was to propose design procedures for the time-dependent behaviour of steel-bars truss slabs accounting for the effects of soffit steel decks. For this purpose, two full-scale slab samples were tested for 9 months, with one slab subjected to non-uniform shrinkage and sustained loading and the other slab subjected to only non-uniform shrinkage. Typical design equations for reinforced concrete slabs and composite steel–concrete slabs were benchmarked against available test results to verify their applicability. Non-linear finite-element models were established to describe the time-dependent behaviour of steel-bars truss slabs, and simplified design procedures were proposed. It was found that the steel-bars truss sample subjected to non-uniform shrinkage had a mid-span deflection accounting for 52·4% of the total deflection; that the design methods in available composite structure standards significantly underestimated the long-term deflections; and that the proposed design procedures well predicted the time-dependent deflections of steel-bars truss slabs by considering the influence of the shrinkage gradient.

Failure Analysis and Reinforcement of 3D-printed Concrete Envelope Structure Based on Phase-field Theory (PFT)

The permanent 3D-printed concrete envelope formwork can realize the personalized printing of special-shaped envelope structures efficiently with a high degree of automation and obvious advantages. This paper calculated the load-bearing characteristics of the 3D-printed concrete envelope formwork and analyzed the influence of steel supports on its load-bearing characteristics based on PFT. The study showed that the structure would have the highest bearing capacity when the position of steel support reinforcement was near the bisected point of the structure and close to the resultant point of the external load; steel support reinforcement could increase the bearing capacity of structures by nearly 5 times; compared with the single support, the double support could increase the same by nearly 3 times; and triple support reinforcement played a limited role in the improvement of the bearing capacity of structures.

Improving the manufacturability of floor slabs by pre-installing elements that partially replace reinforced concrete and formwork

The article discusses well-known and perspective constructive and technological systems for the installation of monolithic and precast-monolithic floor slabs of civil and industrial buildings. It shows examples and expediency of using all kinds of inserts made of plastic and other light materials and products for replacing a part of heavy monolithic reinforced concrete. An original resource-saving method for the installation of precast-monolithic floor slabs with a simultaneous increase in the degree of their construction readiness is proposed. This effect is achieved by reducing their own weight and the use of permanent formwork. Reduction in own weight of the precast-monolithic floor slab is ensured by the use of volumetric lightweight trapezoidal or rectangular inserts, preferably made of expanded polystyrene, during its installation. The use of permanent formwork will eliminate the need for the subsequent performance of labor-intensive finishing and insulation works. To confirm the effectiveness of using the proposed method of precast-monolithic floor slab installation, the operation of two floor slabs was modeled in the LIRA SAPR computing complex - the proposed reinforced concrete innovative slab and a solid reinforced concrete slab. Having analyzed the calculated forces, deformations and the corresponding consumption of reinforcement and concrete, comparative indicators were obtained for the proposed innovative slab and for a typical solid floor slab. As a result, significant savings in material and cost have been proven.

Research on flexural performance of composited RC beams with different forms of TRC permanent formwork

In order to avoid the shortcomings of the traditional building template, such as the cumbersome process of supporting and disassembling the mold, the low turnover, and the occupation of a lot of labor, it is proposed to replace the traditional building formwork with the textile reinforced concrete (TRC) as a permanent formwork. In this paper, the template form is used as the research parameter, and the bending performance of the U-shaped and single-plate TRC template composite beam and the comparative beam under static load is compared and studied. The test results found that during the loading process, the single-plate formwork composite beam was peeled off from the TRC formwork, and the U-shaped formwork and the post-cast concrete interface bonded well. Under the premise that the interface between the formwork and the post-cast concrete is good, the cracking load, yield load and ultimate load of the TRC formwork composite beam are improved compared with the ordinary reinforced concrete beam; the crack width of the composite beam is smaller and the development is slow; Bending rigidity becomes greater but ductility is reduced to a certain extent. Overall, the bending performance of the U-shaped formwork composite beam is better than that of the single-plate formwork composite beam. In addition, on the basis of the test, this paper puts forward the formula of the normal section bending capacity of the U-shaped TRC template laminated RC beam, and the test results are in good agreement with the theoretical calculations.

Computational simulation of eccentrically loaded reinforced concrete walls formed with modular thin-walled permanent formwork system

Stay-in-place formwork (SIPF) systems represent a conventional formwork-free, corrosion-resistant substitute for construction of new reinforced concrete walls. The composite of infill concrete and thin-walled fibre cement board (FCB)/steel studs SIPF consists of a core concrete, filled between two FCBs that are connected to each other using steel studs, embedded to the concrete infill. Similarly, the concrete-filled Polyvinyl Chloride (PVC) hybrid system is comprised of extruded PVC interlocked encasements core-filled with concrete. These lightweight structural SIPFs are utilised in modular construction in which the system is prefabricated in the factory, transported to the site, erected and assembled for concrete casting. Further, the SIPF-encased wall is a composite system that facilitates taking advantage of mixed effects of reinforced concrete and SIPF. These are the major benefits of these systems compared to conventional formwork systems. However, there is a gap in knowledge regarding the strength and ductility measurement of SIPF-encased walls under eccentric axial loads that is presented in this paper. A series of tests was conducted to failure on both composite walls and compared with the reference specimens, i.e. standard walls (STWs). Substantial finite element (FE) studies considering material and geometric nonlinearities as well as contact behaviour are also performed. After a reasonable model verification against test results, a comprehensive parametric investigation accounting for the concrete compressive strength, the thickness of SIPF components (i.e. steel studs, FCB, and PVC), longitudinal bar reinforcement, and axial load ratio is performed. Further, the experimental and numerical results are used to assess the suitability of the theoretical formulation specified in the current Australian Standard (AS3600) for the axial-flexural interaction resistance of SIPF-encased walls. It is demonstrated that the predictions from the current design specifications are overall conservative. Further, it is found that FCB/steel studs SIPF effectively contributes to improve curvature ductility index and axial-flexural strength compared to STWs.

Construction Technology of Enclosing Structures by Means of 3D Printing with One-Stage Polystyrene Concrete

Today, layer-by-layer printing of enclosing structures with a 3D printer is the formation of a permanent formwork from a cement-sand mixture, followed by concreting and thermal insulation of the structure using standard technologies and widespread use of manual labor. Despite the use of robotization, 3D printing is only partially involved in the construction process and does not solve the issue of increasing labor productivity. This, and other disadvantages, hinders its widespread use in construction. 3D printing with one-stage polystyrene concrete is devoid of many traditional printing disadvantages, which allows forming a layer of heat-insulating and structural material over the entire wall width in one pass during the construction process. It was possible to overcome the inhomogeneity of a wall thermal conductivity due to the “cold bridges”, lower layers spread that did not have time to grab and ability to work only at high temperatures. The approbation of the technology is demonstrated its feasibility and opportunities for improvement.

Shear behavior of RC slender beams without stirrups by using precast U-shaped ECC permanent formwork

ECC characterized by its strain-hardening behavior in tension, high tensile and compressive strain and cracking control capacity is an ideal material for permanent formwork of reinforced concrete (RC) beams. This study investigated the shear behavior of RC slender beams without shear reinforcements by using precast U-shaped ECC permanent formwork. A total of 10 beams, including 1 RC beam for reference and 9 beams using U-shaped permanent formwork with different thicknesses and interfacial properties were fabricated and tested. ECC permanent formwork with three different thickness, namely 15, 20 and 25 mm, respectively were precast. At each thickness of permanent formwork, three different interfacial properties, namely smooth interface, anchored interface and rugged interface, respectively were prepared to investigate the effects of interfacial properties. All beams were tested by four-point loading tests to investigate the shear behavior and failure mechanism. The experimental results revealed that the shear carrying and deformation capacities of RC slender beams without stirrups could be enhanced significantly by using U-shaped ECC permanent formwork. The predictive equations for shear carrying capacities of RC beams without stirrups by using precast U-shaped ECC formwork were also proposed based on modified truss model and it agreed well with experimental result.

Peculiarities of erecting walls for houses and buildings by technology of monolithic construction using permanent formwork unit

The article deals with constructive and organizational-technological solutions when performing works on construction of external and internal bearing walls with the use of combined permanent formwork. The technology allows to reduce the construction time by combining in the system of the retained formwork unit three technological processes, which are performed simultaneously by one group of contractors - erection, insulation and wall decoration. Depending on the thickness of the insulation in such houses and buildings, it is possible to achieve close to zero energy consumption.

Design features of low-rise buildings walls erected from permanent formwork ComBlock units

The study focuses on the design of load-bearing monolithic concrete and reinforced concrete walls of low-rise buildings erected from permanent formwork ComBlock units for construction, in areas without episodic influences and analysis of their work. While developing the recommendations the main attention was paid to working out design solutions of load-bearing monolithic walls with minimal reinforcement consumption. The guidelines contain general provisions for the design and calculation of load-bearing vertical elements of a house; numerous studies of the stress-strain state of monolithic vertical load-bearing elements of low-rise buildings with different structural schemes.

Experimental research on compressive behavior of seawater and sea sand concrete-filled RPC tubes

To address the dilemma of structures constructed with seawater and sea sand concrete (SWSSC), including insufficient durability and high cost, an innovative composite column, named SWSSC-filled reactive powder concrete (RPC) tube (SFRPC tube), is proposed and studied. This hybrid system is composed of a prefabricated RPC thin-wall hollow tube with fiber reinforced polymer (FRP) hoops and infilled SWSSC. In order to understand the basic compressive performance of the proposed composite structure, a total of 24 short columns, with 300 mm outer diameter and 600 mm height, were tested in axial compression. SFRPC tube columns exhibited a multi-crack failure mode on the surface of tube without obvious peeling-off of the RPC cover. The RPC tube can serve as the permanent formwork, and maintain its own integrity in the whole loading process, carrying considerable axial load acting on the composite column, due to its super-high compressive strength. The results reveal that the SFRPC tube system effectively utilizes the ultra-high mechanical properties of RPC and FRP confinement effect. Compressive performance of SFRPC tube columns can be further improved as the volumetric FRP hoop ratio in RPC tube increases. It is found that overlapping joint methods for single FRP hoop in RPC tube and the thickness of RPC tube have no significant effect on the mechanical performance of SFRPC tube columns under the current testing conditions. A special confinement model was also proposed for assessing the axial load carrying capacity of SFRPC tube columns.

Experimental behavior of concrete-filled corrugated steel tubular short columns under eccentric compression and non-uniform confinement

Concrete-filled galvanized corrugated steel tubular (CFGCST) column is potentially an economic member to overcome the corrosion of outdoor structures, of which the anticorrosive corrugated steel pipe (CSP) can be used conveniently as the corrosion protection and permanent concrete formwork. The confinement effect provided by CSP essentially contributes to the structural advantages of CFGCST, whilst it, brings about complexities in corresponding load-resisting mechanism. Apart from the non-uniform distribution of stresses of CSP through thickness and height due to its curved shape, the confinement also varies across cross-sectional depth due to eccentric compression. The in-depth understanding and accurate quantification of the confinement effect of such member become a key issue that needs to be addressed. To investigate the impact of confinement on cross-sectional behavior, 24 specimens were tested with 5 load eccentricity ratios and 2 confinement factors. The non-uniformities of confinement along with height and cross-sectional depth were studied based on finite element modelling, validated via measured strains and load bearing capacities. A theoretical derivation was then conducted to characterize the non-uniform confining stress by fully considering the bidirectional curvatures of CSP, as well as the influence of debonding failure on the confinement. In each period of corrugation, the calculation method of equivalent confining stress was proposed based on the uniformization of stresses and geometry.

Precast monolithic coating of an industrial building based on variable-height beam-slabs

We consider the coatings of single-story industrial buildings of frame type, which in a typical solution are made in the form of a flooring of ribbed plates on rafters, trusses or arches. There is a high complexity of manufacturing, transportation and installation of structures and a large height of the coating. We offer truss beams-slabs of box-shaped cross-section, the height of which varies stepwise along the length, being limited by a square parabola at the top. Beams are installed on the substructure structures in a row, and between them on a permanent formwork of wooden boards are arranged monolithic sections of the plate. The calculation of deformations is performed taking into account the inelastic deformation of concrete and rebar in accordance with the recommended norms of state diagrams: three-line for concrete and two-line for rebar. The results of the calculation of a beam-plate with a span of 30 m, which has 5 different stages, the height of which is selected so that the required cross-section of the reinforcement remains constant along the entire length of the structure.