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Concrete is the most widely used construction material. Worldwide consumption of cement, the strength-giving component in concrete, is now estimated to be 4.10 Gt per year, having risen from 2.22 Gt just 10 years ago. This rate of consumption means that cement manufacture alone is estimated to account for 5.2 % of global carbon dioxide emissions. Concrete offers the opportunity to create structures with almost any geometry economically. Yet its unique fluidity is seldom capitalized upon, with concrete instead being cast in rigid, flat moulds to create non-optimized geometries that result in structures with a high material usage and large carbon footprints. This paper will explore flexible formwork construction technologies that embrace the fluidity of concrete to facilitate the practical construction of concrete structures with complex and efficient geometries. This paper presents the current state of the art in flexible formwork technology, highlighting practical uses, research challenges and new opportunities. [ABSTRACT FROM AUTHOR]

One method of forming large openings within hollow-core (HC) floors is to use steel trimmer brackets (headers). These brackets span between slabs on either side of an opening, thereby providing support for a shorter slab. These brackets are referred to in design documents such as the Precast/Prestressed Concrete Institute (PCI) Manual for the Design of Hollow Core Slabs, but no clear guidance is given on their design. While it is clear that the bracket has to support the self-weight of the slab, it is unclear what level of additional live load is supported by the bracket once the concrete keyway joints between the slabs are filled and have gained strength. This paper details a testing program and an extensive finite element (FE) analysis study that have been undertaken to establish the magnitude of live loads applied to the brackets together with the load-transfer interaction at the slab bracket interface. [ABSTRACT FROM AUTHOR]

In this study, the restraining actions induced by stay-in-place metal forms to concrete bridge decks are examined. A comparison between the behaviour of a concrete deck section constructed with regular stay-in-place metal forms and that constructed on a flat-bed geometry where the corrugations in the stay-in-place forms are filled with extruded polystyrene foam is conducted. Data consisting of three-dimensional concrete deck strains, thermal gradient profiles through the deck thickness, deck deflection profiles and reinforcement strains were recorded through a long-term sensory system consisting of 340 sensors embedded within the deck since construction. Analysis of stresses developed in the concrete deck material indicates that using the foam material to fill the corrugations proved to be successful in reducing the concrete shrinkage stresses at early age and also in reducing the constraining effects of the stay-in-place forms on deck expansion and contraction within the monitoring period of about 1 year. [ABSTRACT FROM AUTHOR]

The fatigue performance of concrete bridge decks with glass fiber-reinforced polymer (GFRP) stay-in-place structural forms replacing the bottom layer of rebar is studied. The forms were either flat plate with T-up ribs joined using lap splices or corrugated forms joined through pin-and-eye connections. The decks were supported by simulated precast girders, AASHTO Type III, spaced at 1,775 mm. Two surface preparations were examined for each GFRP form, either using adhesive coating that bonds to freshly cast concrete, or just cleaning the surface before casting. For the bonded deck with flat-ribbed forms, adhesive bond and mechanical fasteners were used at the lap splice, whereas lap splice of the unbonded deck had no adhesive or mechanical fasteners. All decks survived 3 million cycles at 123 kN service load of the CL625 design truck of the Canadian standard. The bonded flat-ribbed-form deck further survived additional 2 million cycles at a higher load simulating a larger girder spacing of 2,365 mm. Stiffness degradations were 9-33% with more reduction in unbonded specimens. Nonetheless, live load deflections of all specimens remained below . The residual ultimate strengths after fatigue were reduced by 5% and 27% for the flat-ribbed and corrugated forms, respectively. However, these strengths remain 7 and 3 times higher than service load, respectively. Both the lap-splice and pin-and-eye connection survived fatigue. Concrete crack width at the top surface over the girders remained below the AASHTO limit of 0.3 mm. [ABSTRACT FROM AUTHOR]

Rock-pocket and honeycomb defects impair overall stiffness, accelerate aging, reduce service life, and cause structural problems in hardened concrete members. Traditional methods for detecting such deficient volumes involve visual observations or localized nondestructive methods, which are labor-intensive, timeconsuming, highly sensitive to test conditions, and require knowledge of and accessibility to defect locations. The authors propose a vibration response-based nondestructive technique that combines experimental and numerical methodologies for use in identifying the location and severity of internal defects of concrete members. The experimental component entails collecting mode shape curvatures from laboratory beam specimens with size-controlled rock pocket and honeycomb defects, and the numerical component entails simulating beam vibration response through a finite element (FE) model parameterized with three defect-identifying variables indicating location (x, coordinate along the beam length) and severity of damage (a, stiffness reduction and b, mass reduction). Defects are detected by comparing the FE model predictions to experimental measurements and inferring the low number of defect-identifying variables. This method is particularly well-suited for rapid and cost-effective quality assurance for precast concrete members and for inspecting concrete members with simple geometric forms. [ABSTRACT FROM AUTHOR]

The concept of casting concrete in fabrics, fabric formwork technology, has resurfaced at various times and in different forms throughout the past century. The following paper traces developments that have used fabrics for concrete formwork, including different types of flexible formwork, controlled permeability formwork and pneumatic formwork. This paper presents a comprehensive historical overview of fabric formwork, listing key innovators, technological developments and their advantages, and offering examples of structures built with these methods. The information gathered is used to present a taxonomy of these related formwork technologies as well as a formal definition of the term 'fabric formwork' that encompasses them. The paper is intended to introduce readers to these technologies and offer readers already familiar with these methods additional historical background. [ABSTRACT FROM AUTHOR]

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A common type of slim floor construction consists of precast prestressed hollow-core slabs supported on the lower flange of transverse shallow steel beams. These structures benefit from slender ceilings, fast erection, a small dead load and a high level of quality. However, the shear capacity of the slabs is considerably reduced due to transverse stresses when they are bedded on slender beams (flexible supports). Apart from unanswered questions regarding safe but economic design, the use of slim floor constructions is hampered because criteria to differentiate between flexible and rigid supports are not yet available. To investigate the effects of different support conditions on shear capacity, full-scale tests on floor systems consisting of ten slabs on flexible supports and reference tests on single slabs on rigid supports were performed. The present paper describes the development and calibration of non-linear three-dimensional finite-element models with the available test data to numerically determine the influence of support type and stiffness on load-bearing behaviour. The results reveal the slabs' failure mechanism and identify a range of flexible supports. [ABSTRACT FROM AUTHOR]

This paper presents the results of experimental investigations on four full-scale precast concrete connections and a half-scale, two-story, two-bay, precast concrete, moment-resisting frame, which consisted of composite concrete beams and cast-in-place concrete columns, under cyclic loading. The precast concrete connections investigated in this paper included an exterior connection, an interior connection, a T connection, and a knee connection. Test results revealed that the four precast concrete connections, as expected, exhibited a strong column-weak beam failure mechanism and failed due to concrete crushing and fracturing of longitudinal bars as a result of forming a plastic hinge at the fixed end of the beam. The four connections behaved in a ductile manner. However, the displacement ductility of the knee connection was the poorest among them. The precast concrete frame exhibited a mixed side-sway mechanism and behaved in a ductile manner. The hysteresis curves of the frame were full and exhibited good energy-dissipation capacity. The global and interstory displacement ductility of the frame was not less than 4.5. In general, the seismic behavior of the precast concrete frame was satisfactory. This research could provide structural engineers with useful information about the safety of precast concrete-frame structures. [ABSTRACT FROM AUTHOR]

The article focuses on the sophisticated design of the prestressed and precast concrete hollow-core beams used for interchange bridge project in San Pedro Sula, Honduras. It mentions that the designer must concentrate on the ease of fabrications, repetition, and ease of assembly to make a cost-effective solution using precast concrete. It presents several photographs and illustrations of the designs of the prestressed and precast concrete hollow-core beams used in the interchange bridge project.

Erection of long, vertical precast concrete members from their as-delivered horizontal position to their vertical position in the structure involves devising handling procedures that protect the safety of the erection personnel while preventing the precast concrete member from cracking during the tilting procedure. The author investigates the most commonly used procedures, three-point and four-point rolling-block lifting systems, and identifies a common instability condition that causes sudden, uncontrolled rolling of the members as they are being tilted toward their vertical position. Methods are devised to detect in any member the potential for such instability, to establish safe location of lifting devices and minimum lengths of crane slings to prevent this condition from occurring, and to analyze and control tensile stresses from causing cracking of long precast concrete wall panels as they are lifted from their horizontal position, rigged for the tilting operation. [ABSTRACT FROM AUTHOR]

Precast, pre stressed concrete box girders are commonly used as superstructure components for short and medium span bridges. Their configuration and typical side-by-side placement make large portions of these elements inaccessible for visual inspection or the application of nondestructive testing techniques. This paper demonstrates that vibration based damage detection (VBDD) is an effective alternative for monitoring their structural health. A box girder removed from a dismantled bridge was used to evaluate the ability of five different VBDD algorithms to detect and localize low levels of spalling damage, with a focus on using a small number of sensors and only the fundamental mode of vibration. All methods were capable of detecting and localizing damage to a region within approximately 1.6 times the longitudinal spacing between as few as six uniformly distributed accelerometers. Strain gauges configured to measure curvature were also effective, but tended to be susceptible to large errors in near support damage cases. Finite element analyses demonstrated that increasing the number of sensor locations leads to a proportional increase in localization accuracy, while the use of additional modes provides little advantage and can sometimes lead to a deterioration in the performance of the VBDD techniques. [ABSTRACT FROM AUTHOR]

The article announces the call for the precast/ prestressed applications for innovative formwork and equipment solutions to join the 47th annual Design Awards Competition for 2009.

Because of superior speed and productivity, slip forms were extensively utilized as a potential formwork candidate in constructing concrete structures for the past few decades. Typical projects that employ this formwork technique are: Core of high-rise buildings, silos, telecommunication towers, cooling towers, heavy concrete offshore platforms, etc. The research presented in this paper aims at studying slip-form application to cores and silos, assessing its productivity, and determining its appropriate speed as well as auxiliary resource combinations. Simulation models are developed in which the potential control units in a slip-form system are described for cores and silos. Data are collected from several case study projects. A set of charts has been developed to predict productivity considering different stoppages, core cross section area, slipping (jacking) rate, and concrete placing methods. These charts play an essential role in managing slip-form application to cores and silos. Results show that the developed simulation models predict the productivity of case study projects with 99.70 and 99.30% accuracy for cores and silos, respectively. The presented research is relevant to both researchers and practitioners. It provides practitioners with charts that assist in scheduling and managing the required resources for slip-form application. In addition, it provides researchers with simulation models and framework for implementing slip forms to core and silo construction. [ABSTRACT FROM AUTHOR]

This paper discusses the mechanical behavior of reinforced concrete columns wrapped with fiber-reinforced polymer (FRP) sheets. A numerical routine was developed to predict the behavior of the columns using a step-by-step technique. The routine is based on an existing model and was modified to account for confinement provided by the traditional steel as well as the external FRP wraps. Several empirical equations for the confined concrete were calibrated with results from experimental tests from different published papers. The most accurate equation was incorporated into the routine to predict the stress-strain relation of the column up to failure. A different confinement to the outer concrete cover and the inner core was used to account for the FRP wraps and the transverse steel. The model was calibrated with experimental results from different experiments on FRP-wrapped reinforced concrete columns.The model was taken one step further by using it to predict the behavior of reinforced concrete columns, with a combination of steel corrosion and CFRP wraps. The columns modeled were subjected to harsh corrosive environment over 44 months. The model successfully predicted the load deformation in both axial and circumferential directions in corroded and intact columns, both wrapped and unwrapped, with good accuracy. The analysis forms a solid foundation for accurate evaluation of the effect of corrosion and wrapping on reinforced concrete columns. [ABSTRACT FROM AUTHOR]

The post-tensioned precast concrete system (PPS) developed in this study consists of U-shaped precast wide beams and concrete columns, where the continuity of wide beam-column joint is provided with the cast-in-place concrete on the U-shaped precast wide beam and the post-tensioning to the beam after casting of slab. The PPS structure can overcome the defect of discontinuity in the connections of precast members using cast-in-place concrete on precast members, and complement the low sectional efficiency of wide beam by applying the post-tensioning. In this study, an experimental investigation was performed with three half-scale specimens of interior connection fabricated employing PPS structure. Specifically, this paper presents the response of PPS interior beam-column joint subjected to cyclic lateral loading and evaluates the relevance of the beam-to-column width ratio criteria specified in ACI 318-05. The test results indicate that the PPS specimens can resist properly seismic loads maintaining overall structural integrity. [ABSTRACT FROM AUTHOR]

According to two-stage (pre-placed aggregate) concrete technology, special grout is injected into forms or foundation trenches with aggregate, as backing, placed earlier. The fresh grout differs from the ordinary concrete mixture. Good quality two-stage grout can be prepared in high-speed mixers, for example an Ultramixer (3000 rpm). It is characterised by high fluidity, low sedimentation, good viscosity, intensive hydration and a notable increase in the cement particles' surface. However, because of the unique and complex equipment involved, two-stage concrete technology is still underutilised. The aimof the investigation presented in this work is to design amixture composition similar in features to Ultramixer grout. For this purpose, the new grout was prepared using a normal mixer (140 rpm) and some admixtures. The experimental tests were performed with different mix proportions. On the basis of the obtained results, an optimal composition has been proposed. A comparison of the new grout features with the properties of the grout produced by the Ultramixer has also been elaborated. The new grout design method can improve two-stage concrete technology. Some preliminary two-stage concrete tests are also presented. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation on the load-bearing capacity of mortar joints used in precast concrete structures. The following variables were used in this research: (a) the type of fill-up material: grout, ‘dry packed’ mortar and without filled-up material; (b) the mortar layer thickness: 15, 22.5 and 30 mm; (c) the ratio of the mortar compressive strength (fm) to compressive precast concrete strength (fc): fm fc; (d) the concrete compressive strength: normal (35 MPa ) and high (60 MPa); and (e) the employment of additional reinforcement in the connection adjacent area. Some of main conclusions are: (a) the most suitable mortar layer thickness is 22.5 mm, which means about 13% of joint width; (b) using mortar with more compressive strength for filling up the connection fm ≥ fc, the mortar joint is not the weak point of the system, but the splitting stress becomes more intense in precast elements; (c) the additional reinforcement at the precast segment end increases the system's ductility as well as restricting the rupture area; however it does not increase the load-bearing capacity of the system. [ABSTRACT FROM AUTHOR]

A modified assembled configuration is introduced for precast concrete frames in which the connections are constructed on the beam span and kept away from the column faces so as to avoid coinciding with the plastic hinge regions during seismic excitations. An experimental study on the seismic performances of two full-scale precast concrete subframes adopting the aforementioned configuration and a monolithically-cast subframe subjected to quasistatic simulated seismic loading is presented. The variable examined was the connection detail. The performances of the precast concrete frames are evaluated on the basis of ductility, energy dissipation capacity, connection strength, and drift capacity. Based on the test results, the precast concrete frames are capable of matching overall performance of the monolithic connections and thereby providing moment-resisting behavior [ABSTRACT FROM AUTHOR]

Details the Israeli formwork standard for concrete as a case study for contemporary trends in formwork standardization. Similarity in the treatment of the design of temporary structures to that of permanent structures; Replacement of the traditional allowable-stress approach with the concept of limit-state design and partial safety factors; Three types of vertical loads that are considered.