Prestressed Beams Research Articles

Flexural behavior of aluminum I-beams strengthened by pre-stressed CFRP tendons

To improve the flexural rigidity and load carrying capacity, aluminum I-beams were retrofitted by pre-stressed carbon fiber reinforced plastic (CFRP) tendons. Three pre-stress schemes were proposed. Four-point-bending experiments were carried out to reveal the flexural behaviors and failure styles of the strengthened beams. Flexure of the pre-stressed beam is greatly reduced due to arch effect and increased flexural rigidity. Increasing the pre-stress level, the flexure gets even smaller. Yield load of the pre-stressed beam is enhanced at a level of 33.3%. CFRP pre-stressing schemes greatly improve the failure load of the aluminum I-beam, which fails at plastic lateral-torsional buckling. The improvement is about 52.3% in this research.

Behavior of prestressed concrete-filled steel tube (CFST) beam

Concrete-filled steel tube (CFST) member is widely used for building, bridge and foundation structures because of its excellent performance. When a CFST member is subjected to axial loads, the filling concrete is confined by the steel tube, resulting in a tri-axial state of compression that improves its strength, stiffness and ductility. However, the cracking of concrete in tension zone would decrease this enhancement when the CFST member is subjected to flexure, especially when it is used as a major flexural member with large-scale section in bridges. To overcome this weakness, the prestressed CFST concept is investigated in this paper. Eight prestressed CFST beams with large-scale section (300×450mm) were tested under bending. Two concrete strengths (C50 and C60) and two different degrees of prestressing (0.26 and 0.40) were studied in the experimental program. The full vibration and grouting method was introduced to gain a good performance of specimens. The perfobond rib shear connector was adopted to achieve the composite action. The flexural behaviors were verified by comparing with predictions from a proposed model considering the confinement effects. A simplified method is proposed to determine the ultimate moment capacity based on the plastic stress block hypothesis. Both experimental and analytical results show that the prestressed strands could significantly enhance the confinement effect of the core concrete under bending, which, in turn, improves the prestressed CFST beam performance in strength, stiffness and ductility.

Moving Load Identification of Small and Medium-Sized Bridges Based on Distributed Optical Fiber Sensing

A novel method was proposed for the moving load identification of bridges based on the influence line theory and distributed optical fiber sensing technique. The method of load and vehicle speed identification was firstly theoretically studied, and then numerical simulation was also performed to study its accuracy and robustness. The numerical results showed that this method was characterized by high accuracy and excellent resistance to noise. Finally, the load identification of an actual continuous pre-stressed concrete beam bridge was carried out with the proposed method. The bridge consists of four pre-stressed box beams. At the same time, a weigh-in-motion system was also installed about 200 m in front of the bridge to measure the speed and moving loads with a purpose of comparing the load identification of the proposed method. Long gauge fiber Bragg grating (FBG) sensors with a gauge length of 1.0 m were adhered to the bottom of the beams. The individual loaded vehicles and the corresponding structure response were mainly monitored as standard samples, and the speed and weight of the sample vehicles were monitored and identified with the proposed method. The results revealed that the distributed long gauge FBG sensors were capable of sensing the structure response precisely and identifying the traffic load. On the basis of the design information and ambient vibration testing results, a refined model was established and the response under unit moving load was acquired for load identification. It was also shown that the sensors in different positions can achieve accurate vehicle speed and weight, the relative error of which are within 10% and 15%, respectively.

Free vibration analysis of pre-stressed FGM Timoshenko beams under large transverse deflection by a variational method

A theoretical study on free vibration behavior of pre-stressed functionally graded material (FGM) beam is carried out. Power law variation of volume fraction along the thickness direction is considered. Geometric non-linearity is incorporated through von Kármán non-linear strain–displacement relationship. The governing equation for the static problem is obtained using minimum potential energy principle. The dynamic problem for the pre-stressed beam is formulated as an eigenvalue problem using Hamilton's principle. Three classical boundary conditions with immovable ends are considered for the present work, namely clamped–clamped, simply supported–simply supported and clamped–simply supported. Four different FGM beams, namely Stainless Steel–Silicon Nitride, Stainless Steel–Zirconia, Stainless Steel–Alumina and Titanium alloy–Zirconia, are considered for generation of results. Numerical results for non-dimensional frequency parameters of undeformed beam are presented. The results are presented in non-dimensional pressure-displacement plane for the static problem and in non-dimensional frequency-displacement plane for the dynamic problem. Comparative frequency-displacement plots are presented for different FGMs and also for different volume fraction indices.

The Application of Equivalent Age Concept to Sand Concrete Compared to Ordinary Concrete

In this research the equivalent age concept was used, in order to simulate strength development of heat treated sand concrete compared with ordinary concrete at different temperature, 35, 55, and 70°C, and validate the simulation results with our experimental results. Sand concrete is a concrete with a lower or without coarse aggregate dosage; it is used to realize thin element as small precast prestressed beams, in injected concrete or in regions where sand is in extra quantity and the coarse aggregate in penury. This concrete is composed by principally sand, filler, superplasticizer, water, and cement. The results show that the simulation of ordinary concrete was acceptable with an error lower than 20%. But the error was considerable for the sand concrete. The error was due to large superplasticizer dosage, which modified the hardening of sand concrete; the most influent parameter in Arrhenius law is apparent energy activation, to search for the value of the activation energy which gives the best simulation; a superposition is used of two curves of different temperature and with superplasticizer dosage 4% and several values of activation energy, 15, 20, 25, and 30 × 10 kcal. The simulation becomes ameliorated with the adequate value of activation energy.

15 m 실규모 프리스트레스트 콘크리트 보에서 2,400 MPa 강연선의 전달길이 평가

In this study, 14.8 m long full scale pretensioned prestressed beam using 2,400 MPa PS strand was fabricated and the transfer length ofthe strand was investigated by measuring strains on nearby reinforcement steel bars. The test results of the beam were compared withsmall size specimen tests with a strand from previous researches (Oh and Kim, 2000; Yim et al., 2015). The full scale test showedsmaller transfer length and smaller difference in the transfer lengths between at cut (sudden release by flame cut) and dead ends thansmall specimens with a strand. Evaluation on the equation of transfer length proposed by Oh et al. (2014), based on test and analysisresults of transfer length of 1,860 MPa strand considering concrete compressive strength and concrete cover depth, was used tocalculate the transfer length of 2,400 MPa PS strand in full scale beam as well as small specimens with a strand. Comparison of theevaluation and test results presented that the equation overestimates the transfer length of 5~9% in small specimen tests, however, morethan 30% in full scale beam specimen for 2,400 MPa PS strand.Key words : 2,400 MPa PS strand, Pretension, PSC, Transfer length

Transient wave velocities in pre-stressed thin-walled beams of open profile with Cosserat-type micro-structure

In the present paper, a new wave theory of thin-walled beams of open profile with Cosserat-type micro-structure is suggested based on the approach proposed by Rossikhin and Shitikova [1] for pre-stressed spatially curved thin-walled beams of open profile. The aim of the authors is to create the theory of propagation of transient waves (surfaces of strong discontinuity) in thin-walled beams of open profile, which should be quite different from Timoshenko-like theories, resulting in the data comparable with those corresponding to transient wave propagation in the three-dimensional Cosserat continuum.

Structural Performance of Prestressed Composite Members with Corrugated Webs Exposed to Fire

In this study, to assess the fire performances of corrugated webbed prestressed (CWPS) composite beams exposed to fire, full-scale fire resisting tests were carried out, and fire-resisting behavioural responses of the test specimens were analyzed and compared with those obtained from nonlinear finite element analyses. Key test variables were the cover thickness of the fire protection material applied to the bottom flange of corrugated webbed steel beams, which was directly exposed to fire, and the shapes of corrugated webs. All the composite beams with fire protection material covers exposed to standard fire showed good fire-resisting capacities with fire ratings over 3 h and in particular, CWPS composite beams with relatively thin fire protection material cover thickness, compared with the non-prestressed slim-floor composite beam, satisfied the required fire performance criteria in ISO 834 standard and Eurocode. Additionally, the test results showed that the shape of corrugated webs used in CWPS composite beam specimens could have a great impact on their fire-resisting performance. The nonlinear finite element analyses performed in this study accurately estimated the overall behaviours of test specimens and especially assessed the effects of the shape of the corrugated web on the temperature distributions and fire resistance performances of CWPS composite beams appropriately.

Analytical investigation of pre-stressed, pre-cast beams with steel pipe sleeves

This paper presents an analytical investigation of the structural performance of a pre-stressed, pre-cast concrete beam with steel pipe sleeves. The hybrid pre-cast beam consists of reinforcing steel, a pre-stressing tendon, pre-cast concrete and cast-in-place concrete. Steel sections are installed at both ends of the beam, and steel pipe sleeves are installed at the locations of pipes. The steel pipe sleeves in the pre-cast, pre-stressed beam allow the installation of piping and facility equipment. A strain-compatibility approach was used to predict the influence of the sleeves and pre-stressing on the structural behavior of the hybrid pre-cast beams. It was found that reinforcing rebar, used to reinforce the sleeve openings for circular steel pipes with a diameter of 125 mm, contribute 20% to the flexural load resisting capacity, suggesting that rebar reinforcement can be considered one of the structural components of the beam. The pre-stressed, pre-cast beam with steel pipe sleeve openings exhibited performance similar to that of beams without openings when the reinforcements placed for the sleeve opening were considered part of the flexural stiffness of the beam.

Matrix Stiffness Method for Composite and Prestressed Beam Analysis Using Linear Integral Operators

In the paper, the analysis of composite and prestressed beams using the matrix stiffness method is presented. The stiffness matrix for the frame element with a moment release at one end and the vector of equivalent nodal forces for the frame element with and without a moment release are derived. In the presented method, concrete is assumed to behave as viscoelastic material and the relaxation of the prestressing steel is also considered. Therefore, the relations between the generalized element displacements and the generalized element forces are integral and, here, are presented using the mathematical operators. Applying the linear integral operators, the solution to the problem is derived without introducing additional mathematical approximations and simplifications, besides the inevitable approximations related to the rheological properties of constitute materials, i.e., steel, concrete, prestressing and reinforcement steel. The derived relations can be applied with any concrete creep functions and for the element with a variable cross section.

Experimental Study on the Mechanical Property of SMA Externally Prestressed Concrete Box Beam

This paper conducted an experiment to research flexural property of SMA unbounded prestressed box beam ,which applied the Shape Memory Alloy (SMA) at martensite state as externally prestressing tendons, and then through heating the SMA bars fully anchored on the beam with cracks by electrifying motivation, drove SMA to produce the “recovery stress” because of transformation, to study the effects of this stress on the deflection and crack width of concrete box-beam on work ,to study the recovery ability of SMA bars ,and to provide basis for the application of the SMA bars to bridge strengthening.

Vulnerability assessment and retrofit solutions of precast industrial structures

The seismic sequence which hit the Northern Italian territory in 2012 produced extensive damage to reinforced concrete (RC) precast buildings typically adopted as industrial facilities. The considered damaged buildings are constituted by one-storey precast structures with RC columns connected to the ground by means of isolated socket foundations. The roof structural layout is composed of pre-stressed RC beams supporting pre-stressed RC floor elements, both designed as simply supported beams. The observed damage pattern, already highlighted in previous earthquakes, is mainly related to insufficient connection strength and ductility or to the absence of mechanical devices, being the connections designed neglecting seismic loads or neglecting displacement and rotation compatibility between adjacent elements. Following the vulnerabilities emerged in past seismic events, the paper investigates the seismic performance of industrial facilities typical of the Italian territory. The European building code seismic assessment methodologies are presented and discussed, as well as the retrofit interventions required to achieve an appropriate level of seismic capacity. The assessment procedure and retrofit solutions are applied to a selected case study.

Mechanical Analysis and Economic Research of RPC Beam Bridge

RPC(Reactive Powder Concrete) is a kind of high performance concrete which has many excellent mechanical properties, e.g. ultra-high-strength, high tenacity and good durability, and it has been applied in engineering practice. However, at present the economic research about RPC bridge is few at home and abroad, which has hindered the development of RPC bridge to some extent. By means of the mechanical analysis and economic research about NC(normal concrete ) beam bridge of pre-stressed steel strand (the span is 40m), RPC beam bridge of pre-stressed steel strand and RPC beam bridge of pre-stressed CFRP(Carbon Fiber Reinforced Polymer) tendon after the sectional optimization has been done, this paper reach the conclusion that the RPC beam bridge can greatly reduce the sectional size of beam bridge and reduce the weight by 23.7% , besides, the total cost of RPC beam bridge of pre-stressed steel strand is almost same with the total cost of NC beam bridge during the entire service period of bridge. Therefore, considering the long-term perspective, the integrated economy of RPC beam bridge of pre-stressed steel strand is good.

Analytical Approach to Predict Pre–Camber Deflection of the Pre-stressed Glulam Beams

A new approach to reinforce glulam timber beams using compressed wood (CW) has been developed by the Author. The compressed wood blocks are inserted into pre-cut holes on the top of glulam beams to produce pre-camber and to generate initial tensile and compressive stresses on the top and on the bottom extreme fiber of the glulam beam, respectively. A simple analytical approach has been developed to predict pre-camber deflections of the beams reinforced with three CW blocks. Assuming that moisture-dependent expansion of the CW block creates an interactive linear pressure between the glulam beam and the CW block, this would generate a pair of eccentric force away from the neutral axis of the beam. It is shown that the pre-camber deflection predicted at midspan of the short beams with various reinforcing arrangements give good agreement with the measured pre-camber from previous experimental results.

Dynamic analysis of pre-stressed elastic beams under moving mass using different beam models

This study presents dynamic analysis of pre-stressed elastic beams under the action of moving mass loads by using Bernoulli-Euler, Rayleigh, and shear beam models. It is assumed the mass moves with a constant speed and is in continuous contact with the beam during its motion. Discrete equations of motion with time-dependent coefficients are obtained by using the assumed mode method for each beam models considered. Numerical calculations are made by Newmark method to obtain dynamic response of the beam. Effects of the pre-stressing force, rotatory inertia and transverse shear on the results for the dynamic deflection and bending moment of the beam and the interaction force between the mass and the beam are studied by depending on mass weight and speed of the moving mass.

Performance of non-prismatic simply supported prestressed concrete beams

Prestressing is the most commonly employed technique in bridges and long span beams in commercial buildings as prestressing results in slender section with higher load carrying capacities. This work is an attempt to study the performance of a minimum weight prestressed concrete beam adopting a non-prismatic section so that there will be a reduction in the volume of concrete which in turn reduces the self-weight of the structure. The effect of adopting a non-prismatic section on parameters like prestressing force, area of prestressing steel, bending stresses, shear stresses and percentage loss of prestress are established theoretically. The analysis of non-prismatic prestressed beams is based on the assumption of pure bending theory. Equations are derived for dead load bending moment, eccentricity, and depth at any required section. Based on these equations an algorithm is developed which does the stress checks for the given section for every 500 mm interval of the span. Limit state method is used for the design of beam and finite difference method is used for finding out the deflection of a non-prismatic beam. All the parameters of nonprismatic prestressed concrete beams are compared with that of the rectangular prestressed concrete members and observed that minimum weight design and economical design are not same. Minimum weight design results in the increase in required area of prestressing steel.

Experimental investigation of the snap-through buckling of electrostatically actuated initially curved pre-stressed micro beams

The experimental study of the stability properties of initially curved micro beams subjected to an axial pre-stressing load and transversal deflection-dependent distributed electrostatic force is presented. The devices were fabricated from single crystal silicon on insulator (SOI) wafer using deep reactive ion etching (DRIE). The in-plane quasi-static beam response was video recorded and analyzed by means of image processing. The beam behavior was theoretically predicted using a reduced order model with the axial pre-stressing force assessed on the basis of the deviation of the beam actual initial curvature from the nominal designed one. The experimental results are consistent with the theoretical symmetric and asymmetric snap-through buckling criteria.

Experimental Verification of Pre-Stressed Beams

The paper is a follow-up to previous presentations regarding the experience with ultra-high-performance (UHPC) concrete in the Czech Republic. It will present specific production and testing of pre-stressed beams in the company Skanska a.s. In 2013, the manufacturing facility of the company Skanska a.s. in Štětí, the Prefa plant, produced several series of pre-stressed beams made of ultra-high-performance concrete. The last series of pre-stressed beams was kept in a storage facility in Štětí over winter. In February 2014, destructive tests were carried out on two of the beams in the Štětí facility directly. Another two beams are used for monitoring the long-term changes under continuous load. A description of the tests and their results will be published in the paper. At the same time, a number of accompanying tests were carried out in the Klokner Institute of ČVUT in Prague. The results of these tests will also be mentioned in this paper. The experience and results have been achieved thanks to the grant project no. TA01010269 “Applied research of ultra-high-performance concrete (UHPC) for precast units of structures” subsidized by the Technology Agency of the Czech Republic.

Assessment of shear capacity methods of steel fiber reinforced concrete beams using full scale prestressed bridge beams

Steel fiber addition in concrete is widely known to increase the non-flexural performance of concrete structures such as shear capacity. Design guides such as fib Model Code (2010) have recognised this effect and that these guidelines may become widely accepted. The current design guides are based on laboratory scale tests which may be compromised by the scale effects. This paper reports the results of full sized precast prestressed bridge beams that were fabricated and tested to shear failure. Two beams had steel fiber and two beams were plain concrete. None of the beams had any vertical shear reinforcements. The addition of steel fiber at the dosage of 60 kg per cubic metre resulted in more than twice the shear capacity as compared to the beams without steel fibers. The results of the fiber reinforced beams were compared with the calculated shear capacity of the fib Model Code (2010) and plastic design method. This paper presents a method to include prestress in previously developed plastic design method. The model code method predicted an increase of shear capacity of 22 % as compared to the experimental results of 112 % increase due to steel fiber addition. This demonstrates that the model code is not effective in taking into consideration of the contributions by steel fibers. The plastic design approach predicted an increase of shear capacity of 122 % which is close to the experimental values. Based on this full scale tests, the plastic design approach appears to be more suitable for estimation of shear capacity enhancement when steel fibers are used.

Dispersion and localisation in structured Rayleigh beams

This paper brings a comparative analysis between dynamic models of couple-stress elastic materials and structured Rayleigh beams on a Winkler foundation. Although physical phenomena have different physical origins, the underlying equations appear to be similar, and hence mathematical models have a lot in common. In the present work, our main focus is on the analysis of dispersive waves, band-gaps and localised waveforms in structured Rayleigh beams. The Rayleigh beam theory includes the effects of rotational inertia which are neglected in the Euler–Bernoulli beam theory. This makes the approach applicable to higher frequency regimes. Special attention is given to waves in pre-stressed Rayleigh beams on elastic foundations.