Bending Members Research Articles

To the design of the deflections of flexural concrete members reinforced with fiber-reinforced polymer bars

Introduction. Fiber-reinforced polymers (FRP) reinforcement has a relatively low modulus of elasticity compared to steel. In this connection, the bent members with such reinforcement have a higher deformability. The stress-strain diagram for FRP under short-term loading is almost straight and does not have a yield line, as in steel reinforcement. At the same time, modern methods of calculating structures with for FRP reinforcement are based on existing approaches for reinforced concrete structures. In this regard, the current direction for study is to assess the reliability and improve the existing methods for calculating members with FRP reinforcement for the serviceability limit states.
 Materials and methods. Experimental studies were carried with regard for and in compliance with the provisions of National State Standard 8829-94. Tested samples represented concrete beams that were 1,810 mm long and had a cross section of 120 × 220 mm. Their tensile side was reinforced with two bars. Steel, glass fiber-reinforced polymer (GFRP) and basalt fiber-reinforced polymer (BFRP) bars were used to reinforce the beams. The value of the reinforcement ratio varied. Deflections calculation methods, applied according to Construction rules and regulations 295.1325800.2017 (Russia) and ACI 440.1R-06 (USA) were analyzed.
 Results. The results of the theoretical and experimental studies of the deformability of flexural members having FRP reinforcement are obtained. The inaccurate determination of the cracking moment Mcrc has a negative impact on the results of the deflection calculation. The deviation of the theoretical values of the cracking moment according to the method of Construction rules and regulations 295.1325800.2017 from the experimental ones is 26.2–59.1 %, in the method of ACI 440.1 R-06 — 20.1–57.1 %. For the ACI 440.1 R-06 method, the calculation is more accurate, in which the short-term deflection was multiplied by the factor λ = 0,6ξ = 0,6 · 2 = 1,2, for the Construction rules and regulations 295.1325800.2017 method — when using ψf = 1 – 0,8Mcrc / M.
 Conclusions. The results obtained showed the need to improve the considered calculation methods. To increase the accuracy of the calculation of deflections according to the method of SP 295.1325800.2017, at the first stage, it is possible to approximate the theoretical values of the cracking moment to the experimental data by introducing correction factor in the equation according to the calculation of Mcrc: for beams with a GFRP high-bond bars — 0.7, for BFRP with a sanded surface — 0.5.

Flexural characteristics of Eucalyptus nitens timber with high moisture content

The demand for timber resources in the building industry has been increasing. Plantation Eucalyptus nitens is of interest because of its sustainable supply and potential for structural applications. However, few design standards cover strength values of plantation eucalypt timber, especially flexural failure below and above the fibre saturation point, which is an important mechanism of failure in bending members used in the building industry. Static bending tests were undertaken using a universal testing machine to examine nonlinear bending behaviour of 130 fibre managed E. nitens small clear wood samples at low and high moisture contents (MC). The mean bending modulus of rupture (MOR) was 80.7 MPa for low MC and 59.0 MPa for high MC. The high MC samples exhibited larger displacements at low ultimate loads, while the low MC samples showed abrupt failures at relatively small displacements with high ultimate loads. The design characteristic values for low and high MC E. nitens were 68.5 MPa and 39.8 MPa, respectively. This research demonstrates that fibre managed E. nitens timber is a promising timber for structural applications, especially when exposed to water, as the MOR reduction of E. nitens timber above FSP is relatively lower than those of P. radiata, which is a traditional construction material.

Experimental investigation into the mechanical properties of scrimber composite for structural applications

Scrimber composite is a novel engineered wood-based construction material that is manufactured by reconstituting structural lumber using small-diameter tree species. In this study, clear specimens of the scrimber composite made from fast-growing poplar trees were tested to comprehend their mechanical properties; besides, a group of full-scale scrimber beams was tested to acquire the bending properties of structural-scale scrimber bending members. Then, comparison of mechanical properties was conducted among this scrimber composite, other common engineered wood, and bamboo scrimber. Finally, simplified longitudinal stress–strain models were proposed based on the experimental stress–strain relationships of the scrimber composite under the parallel-to-grain tension and parallel-to-grain compression scenarios. Results show that the scrimber composite can provide ideal mechanical properties, which are comparable or even superior to those of other common engineered wood/bamboo products. For the scrimber under the parallel-to-grain or perpendicular-to-grain compression, it is featured by ductile failure modes, such as crushing failure at the compressive zone and splitting failure with fractures propagating along the grain; whereas, for the scrimber composite under the shear, tension, and bending scenarios, it is featured by brittle failure modes, such as tension failure with flat fractures and shear failure along the bonding surface. Besides, it is proven that using the design strength of the clear specimens of the scrimber is reasonable and conservative for the design of structural-scale scrimber bending members. For the scrimber under the parallel-to-grain compression, the nonlinear characteristics of its stress–strain relationship can be described by one fourth-order polynomial function.

Estimation of the residual resource of wooden structures by changing geometric parameters of the cross-section

In this article, the authors propose a method for assessing the residual resource by changing the geometric parameters of wooden structures. A general formula for estimating the maximum service life is presented. Then a number of special cases are considered when calculating the ultimate service life for the first group of limiting states. As a result, formulas were derived for calculating the ultimate service life for various design cases: centrally tensioned, centrally compressed, bending members, members subject to an axial force with bending. The author considered the determination of the rate of change in geometric parameters at the macrolevel (visually observed changes) and microscopic (microcracks, breaks of bonds between atoms). Formulas for determining the rate of change of geometric parameters at the macro and micro levels are proposed. The advantages and disadvantages of this method are presented. The scope of its application is indicated.

Experimental Study on Shear Behavior of Reinforced Autoclaved Aerated Concrete Slab

Process two-points concentrate force load shearing trial for 6 ALC plates (Autoclaved aerated concrete reinforced plate), the article introduced the trial specimen structure, trial device and load scheme. This trial obtained the influence of the shear capacity of ALC plate like failure mode, load-deflection curve, stress (varying) distribution, steel types and shear span ratio. The research shown that: ①The reinforced ALC plate easily form the strong bending and weak shearing members, happen shear pressure failure when designed shear span ratio X=2.5, happen diagonal-tension failure, when designed shear span ratio X>5; ②If the oblique crack position close to the anchoring gusset or pass through anchoring section then maybe weaken the anchoring force and reduce the shearing strength of plate. Because of its brittle nature, anchorage failure must be avoid. Sufficient anchorage can theoretically be provided either by bond or by cross bars welded to the longitudinal reinforcement. ③For the calculation method of the shear bearing capacity of ALC without shear reinforcement with high strength longitudinal steel reinforcement, the technical code for the application of autoclaved aerated concrete in building in China is no longer applicable, EU standards calculated result are all less than the measured values, the method of international RILEM materials association is more suitable and the calculated value more close to the measured value.

Seismic behavior of ultra-high performance concrete long columns reinforced with high-strength steel

In this study, the cooperative working mechanism of high-strength steel and ultra-high performance concrete (UHPC) was investigated. Five UHPC columns were tested under reversed loading, including three UHPC columns reinforced with high-strength steel, one UHPC column reinforced with normal-strength steel and one UHPC column reinforce with normal-strength steel and confined by carbon fiber reinforced polymer (CFRP) sheet. The results show that all the columns failed in bending mode. High-strength reinforcement can restrain UHPC effectively and improve the initial stiffness, ductility and bearing capacity of the test columns. The larger stirrup spacing can result in earlier cracking and lower the bearing capacity of the test column. The CFRP sheet can provide effective confinement for the UHPC, which can improve the yield and ultimate displacement of the test columns. However, it has little contribution to the bearing capacity. A flexural model has been developed for the analysis of UHPC bending members, and the results from the model are in good agreement with the experiment data.

Experimental study on flexural behavior of light steel hollow flange beam with various stiffening arrangements

Nowadays, cold-form steel section is widely used in the construction of steel structure as they proved more efficient as compared to the hot-rolled section. The steel beams are also called as bending or flexure members and are susceptible to lateral torsional as well as distortion buckling, which ultimately leads to reduction in moment of resistance of the sections. To conquer this light steel beam (LSB) is developed. Observation on failure pattern of light steel beam from the previous research shows that it becomes essential to strengthen the flexural members. Therefore, in this study an attempt has been made to study the effectiveness of various strengthening alternatives of the LSB, i.e., the section with and without notch and provision of stiffeners at web and flange. As a result, flexural strength, failure pattern and deflection parameters have been studied. To validate the failure patterns and deflection, the beam specimens were analyzed using ANSYS v 12. The experimental and finite element results reveal that there is an increased in bending strength of 25.6% when the stiffener is provided on web as compared to the other stiffening arrangements. For that reason, an intermediate web stiffening arrangement is found to be better than the intermediate flange sections.

Mechanical performance of laminated veneer lumber and Glulam beams after short-term incident heat exposure

Timber use is becoming more appealing in the recent years especially ‘exposed timber’; however, the information available on the performance of engineered timber after fire is limited. This paper explores the performance of timber elements exposed to well defined thermal boundary conditions and examines the extent of adhesive degradation after heating. Two different types of timber beams are explored; ‘glued laminated timber’ (Glulam) and ‘laminated veneer lumber’ (LVL). A subset of beams was exposed to radiant heat as per a modified ASTM E1321 heating procedure. An additional subset of beams also had an area of their cross-section carved away, equivalent to the char depth of the heated beams. The carved beams allow for the identification of degradation beyond the char layer, as theoretically both the carved and charred beams would have the same effective cross-sectional area. All beams were mechanically loaded to failure using a four-point loading setup. While the current allowance for degradation beyond the char layer is considered to be 7 mm for exposure times of 20 min and greater [1], the results herein indicate that for bending members this layer extends to at least a minimum of 11.7 mm for LVL and 12.3 mm for Glulam. The aim of this paper is to assess the post-fire performance of Glulam and LVL through looking at strength loss due to adhesive degradation, which may contribute towards enabling tall and unencapsulated engineered timber buildings.

An investigation of the influence of the reduced elasticity modulus on strength of pultruded frp members in bending

The polymer composite known as Fibre Reinforced Polymer (FRP) has several advantages over conventional materials. It has been slowly incorporated into civil infrastructures, because the general regulations have not yet been officially introduced. Pultruded FRP manufactures have internal standards of organizations and Guidelines. Therefore, the design identifies issues that require clarification. This study presents influence of the reduced elasticity modulus on strength of pultruded FRP members in bending with a symmetrical cross-section. The position of the neutral line and calculation of strength and deflections with and without reduced modulus of elasticity are determined in the study. Comparison of the results of calculations showed that when taking into account the reduced modulus of elasticity, the deformability is reduced by up to 15 %. The significance of the results obtained for the construction industry consists in the possibility of a refined calculation of the flexural pultruded FRP members taking into account the reduced modulus of elasticity in order to effectively use the strength reserves and reducing material consumption.

The Sustainability Performance of Reinforced Concrete Structures in Tunnel Lining Induced by Long-Term Coastal Environment

At present, the damage caused by steel corrosion to structures has become a serious problem all over the world. In order to study the mechanical behaviors of tunnel lining structure system under the corrosive environment to rebars, first, the bending tests were performed to investigate the crack propagation behavior and structural bearing capacity of the reinforced concrete bending members degraded by corrosion. Secondly, the pull-out tests were performed to investigate the degradation of bonding strength between corroded rebars and the concrete. Finally, on the basis of the findings from the pull-out tests, a 3-D finite element bond-slip model of reinforced concrete lining structure has been established to simulate the changes of bearing capacity and durability of tunnel reinforced concrete lining under different corrosion degrees. The research has revealed: Rebar corrosion is the most important factor affecting concrete and steel corrosion. As the conversion rust rate increases, the ultimate drawing force continues to decrease. With the increase of the corrosion rate, the deflection of the specimen when it is destroyed becomes smaller, the cracking load becomes smaller and the bearing capacity also decreases. As the degree of corrosion increases, the overall deformation of the tunnel increases, and the overall safety of the lining structure decreases. The corner position is the most prone to problems after the lining structure is corroded, so pay more attention. As well, the safety of the lining structure will be basically lost when the final corrosion rate of the steel bars is greater than 30%. The findings of this research can be used to evaluate the corrosion degree of tunnel reinforced concrete lining structure and support the durability design of new tunnel concrete lining structure.

Experimental Investigation of Fatigue Debonding Growth in FRP-Concrete Interface.

An externally bonded fiber reinforced polymer (FRP) plate (or sheet) is now widely used in strengthening bending members due to its outstanding properties, such as a high strength to weight ratio, easy operating, corrosion and fatigue resistance. However, the concrete member strengthened by this technology may have a problem with the adhesion between FRP and concrete. This kind of debonding failure can be broadly classified into two modes: (a) plate end debonding at or near the plate end, and (b) intermediate crack-induced debonding (intermediate crack-induced (IC) debonding) near the loading point. The IC debonding, unlike the plate end debonding, still needs a large amount of investigation work, especially for the interface under fatigue load. In this paper, ten single shear pull-out tests were carried out under a static or fatigue load. Different load ranges and load levels were considered, and the debonding growth process was carefully recorded. The experimental results indicate that the load range is one of the main parameters, which determines the debonding growth rate. Moreover, the load level can also play an important role when loaded with the same load range. Finally, a new prediction model of the fatigue debonding growth rate was proposed, and has an excellent agreement with the experimental results.

GFRP管–钢骨混凝土纯弯构件的滞回性能研究

GFRP管–钢骨混凝土纯弯构件的滞回性能研究

Steel Structures Research Update: Advances in Design with Hollow Structural Steel Members

Recent advances in design of steel-frame systems with hollow structural steel (HSS) members are highlighted. The featured work includes new and updated design guides that are co-authored by Jeffrey Packer and Jason McCormick. Dr. Packer’s experimental, numerical, and analytical research informs the design of HSS for various loading conditions, with a bias toward code/specification-related issues and guidance for practicing engineers. Dr. McCormick’s research on HSS members and connections ranges from research on steel HSS-based seismic moment frames to the use of innovative materials (e.g., polymer foam) to control the structural response of HSS members under seismic and wind loads. Selected studies are featured along with a preview of the new design guides. Research on HSS columns under axial and lateral loads fills knowledge gaps in seismic behavior and design. Foam-filled brace and bending member experiments show improved seismic performance with a light-weight polyurethane fill. Field tests, laboratory experiments, and numerical modeling are used to study behavior and develop design methods for hollow and concrete-filled HSS subject to blast and impact loading. Research on single-sided fillet welds of HSS members leads to improved design recommendations. Improved design procedures are also recommended based on research on HSS connections that are in branch compression, near chord ends, or offset laterally.

Reinforced Concrete Beam with Light Weight blocks and Steel Fibre added below Neutral Axis

The reinforced concrete is one of the widely used structural materials which have its own major advantages and disadvantages. Its behaviour when provided in various positions in the structural elements like compression, tension, and shear zones has significant impact. Since the concrete is excellent in the compression behaviour, and only a nominal performer in the tension behaviour, steel reinforcement are provided in required zones where tension occurs. Thus in a bending member, below the neutral axis, that is at the tension zone, the concrete acts only as a interface medium between reinforcement that carrying the tension and the concrete above neutral axis carrying compression forces. This concrete is also called as sacrificial concrete. Thus in order to efficiently use the concrete falls under the tension zone, the concrete can be swapped with any suitable lighter or cheaper material or the concrete may be strengthened to carry tensile stresses. In this present study, the concrete below neutral axis is replaced with lightweight ‘aerocon’ block cubes of 8 cu.cm and 64 cu.cm by 20% of volume of concrete and in another specimen, steel fibres are added in the concrete that are below neutral axis by 2% and 3% by weight to improve the local tensile strength of concrete as material The results obtained shows that the aerocon cubes replaced specimens has equivalent performance of the control specimen and the steel fibre added specimen had superior deflection and crack performance than the control specimen.

Anchorage length of reinforcing bars in tension: an assessment of the Australian Standard AS 3600:2018

When designing a reinforced concrete member for strength, ductility and robustness, it is essential that a sufficient length of reinforcement is developed on both sides of a critical section in a zone of tension. The specifications of the existing codes of practice for calculating the development length of reinforcement are statistically based on test data mostly from small-scale pull-out and beam specimens, and their applicability outside the range of the test data is uncertain. This paper describes an experimental research program to assess the effects of different structural parameters on the development length requirements for modern high strength steel reinforcing bars, including the case of lapped splices in large-scale reinforced concrete members in bending. The factors of safety obtained in the tests are assessed according to the Australian Standard (AS3600:2018) provisions for the anchorage length of reinforcing bars in tension and also in terms of attainable average bond stress in different anchorage conditions. The study has revealed that modification(s) to two of the coefficients included in the provisions of AS3600:2018 would provide a more consistent and reliable factor of safety for the anchorage of reinforcement in large-scale concrete members, including at lapped splice locations.

Safety Assessment of Eurocode 3 Stability Design Rules for Prismatic Members in Bending and Compression

This paper presents the safety assessment of Eurocode 3—part 1-1 (Eurocode in EN 1993-1-1, Eurocode 3: design of steel structures—part 1-1: general rules and rules for buildings, CEN, Brussels, 2005) rules for hot-rolled members with I and H cross-sections loaded in bending and compression. The safety assessment follows the recommendations of Annex D of EN 1990 (Eurocode in EN 1990, Eurocode—basis of structural design, CEN, Brussels, 2002). It is based on a large number (11,345) of numerical simulations (GMNIA) covering various relevant parameters. The assessment aimed at the justification of the partial factors to be used in the design of members under bending and compression as part of the ongoing process of revision of Eurocode 3—part 1-1. For that, it covered the application of the interaction factors given in Annex B/Method 2 of the current version of Eurocode 3—part 1-1 which will be the only method in the future version of Eurocode 3. In addition, the interaction factors were applied with the new buckling curves for lateral-torsional buckling, as they will appear in the new version. The assessment showed consistent results across the subsets considered with low variability and partial factors generally lower than 1.0. Finally, the γM* values are compared for flexural buckling of columns, lateral-torsional buckling of beams with the results obtained for beam-columns considering fy, cross-section geometry and E as random variables, using the same statistical characterization of the random variables. It is observed that the partial factors obtained beam-columns are lower than those obtained for columns and beams. In conclusion, based on combination of the results obtained it was possible to recommend a global value of γM1 = 1.0.

College of Falkonergården, Frederiksberg, Denmark: Structural and architecturally innovative multifunctional steel hall

AbstractThe new multifunctional hall of Falkonergårdens Gymnasium and the associated foyer opened in 2015 and can be used by up to 1,000 people. The same year, it was awarded a prize by Frederiksberg Municipality as one of the city's finest buildings. In 2016, the building also received this year's “Store Arne”, awarded annually by the Danish Association of Architects for work that raises the standards of architecture in Copenhagen.The ‘multihall’ for Falkonergården in Copenhagen has a covered steel structure. It is a structure that maximizes the use of the shape with interacting plate action and “membrane” action in the cylindrical walls. The basic structural behavior is without use of primary structural members in bending. It has an orthogonal space structure for the upper roof; it has no horizontal bracing, but is only stabilized for horizontal shear forces by a closed kidney‐shaped ring beam without bending. The structural spaceframe roof has maximized the production possibility of the use of large fully fabric‐welded trusses bolted together on site with welded plane cross members. The structural design of the roof space frame allowed erection in only two days without use of scaffolding. Very simple structural freeware has been a help in the sketch design stage.The aim of the steel design was to find a synthesis of architecture, structural behavior, productivity and buildability. It was a very challenging job, although full understanding is only for people with X‐ray eyes! (Fig. 1 and 2).

Seismic Behavior Effect of Knee Braced Frames Considering Different Type of Geometry under Non-Linear Analysis

The design and behavior of a ductile structural system called a knee-braced moment frame are presented in this paper. The design of this structural system is based on a capacity-design concept that results in ductile behavior. The knee part is a fuse-like component that dissipates energy by the formation of plastic flexural and/or shear hinges at its ends and mid-span, when the building is subjected to severe lateral loads. However, the diagonal brace component, on the other hand, provides the required level of lateral stiffness and remains in the elastic range without buckling at any time. Attempts have been made, in the present study, to investigate the non-linear seismic behavior of Knee-Braced Frame systems for various influencing factors, and to formulate the effects of the number of building stories, the length of the knee element, and moment of inertia of the bending members on the seismic behavior, the drift of the stories, and the failure mode of these systems. Finally, based on the results of the study, some recommendations have been offered for the effective range parameters for the optimal performance of these systems.

Flexural rigidity of cold-formed steel built-up members

Cold-formed steel (CFS) built-up members are formed by connecting several single members by fasteners. This paper presents experimental, numerical and analytical studies on the effect of fastener configurations on the flexural rigidity of built-up sections. In this research, two zinc-coated steel C-sections are connected back-to-back to form a double-web built-up I-section, which is subject to weak-axis bending. A closed-formed expression for the flexural rigidity of built-up sections as a function of fastener stiffness, number and position of fasteners, and section geometry is then derived. This is validated against the tests and finite element modelling, and can be adapted more generally to determine the stiffness and global strength of CFS built-up members in bending.

Material characterization of high-toughness steel

Designers have long recognized the inherent structural efficiency and economy associated with non-redundant bridge systems. Presently, steel bridge structures with non-redundant tension members, labeled as fracture critical members (FCMs), are subjected to more stringent design, material, fabrication, and inspection requirements. FCM requirements are contained in the AASHTO/AWS Fracture Control Plan (FCP) and Code of Federal Regulations (CFRs). The consequence of the requirements, in particular as related to the associated in-service inspection costs, is a higher life-cycle cost when compared to redundant steel bridge structures. However, significant advances have been made over the past 40 years since the original AASHTO/AWS FCP was introduced. Advances in the understanding of fracture mechanics, material and structural behavior, and fatigue crack initiation and growth as well as advancements in fabrication and inspection technologies have allowed other industries to address fracture in a more integrated manner. One-step toward an integrated FCP is to take advantage of the superior fracture toughness of modern steels. While increased fracture toughness is a performance benefit often highlighted for modern steels, there is a lack of fundamental test data and material characterization studies. A large test program was conducted focused on the use of high-toughness steels routinely used in bridge fabrication to establish rational inspection intervals for members traditionally classified as fracture critical. The project was comprised of small-scale material testing, full-scale fracture testing of steel bridge axial and bending members, three-dimensional finite element modeling, and an analytical parametric study. Material characterization results, which included tensile testing, chemistry, Charpy v-notch (CVN) impact testing, percent shear measurement, reference temperature determination, and ductile tearing initiation testing, are presented. Test results showed some of the steels tested demonstrated larger than expected CVN scatter in the transition region. Most importantly, the research revealed for the steels tested the master curve created using Charpy-sized SE(B) specimens resulted in an overestimate of fracture toughness compared to 1 T SE(B) specimens.