Lattice Girder Research Articles

Evaluation of the flexural stiffness of a lattice girder composite slab at the construction stage according to the lattice girder shape

Lattice girder composite slabs (LGCS) for use in construction stages are structures in which part of the lattice girder is embedded in precast concrete panels with a thickness of less than 100 mm. they serve as a permanent formwork supporting the casting loads of on-site concrete while constituting a portion of the RC slab. In this study, analytical research was conducted to evaluate the flexural stiffness of LGCS effectively and simply considering a range of variables. Based on the results, an Euler-Bernoulli beam-theory-based equivalent sectional analysis method is proposed. To achieve this, the study extracted the second moments of area (Iexp) from the experimental results of previous researchers and compared them with the second moments of area (Ibeam) calculated using the Euler-Bernoulli beam-theory-based sectional analysis, analyzing how the ratio (Ibeam/Iexp) varies according to the design parameters. Variable analyses over a wide range were conducted by expanding the types and ranges of variables, and the effects of different variables and ranges were analyzed by comparing the second moments of area based on an FE analysis of LGCS (IFEM) with those based on a beam analysis (Ibeam). Furthermore, to apply the equivalent sectional analysis method to LGCS, equivalent second-moment-of-area formulas were proposed through the equivalent neutral axis and equivalent arm length for each sectional element.

Improved Subsidence Assessment for More Reliable Excavation Activity in Tehran

This paper presents a particular tunneling method, the new Austrian tunneling method (NATM), which plays an important role in reducing subsidence of the surface and damage to structures in urban areas. It has a wide range of applications in shallow tunneling projects all over the world. In this study, numerical modeling of the third-line Metro tunnel in Tehran, which is designed and stabilized by the NATM, is under discussion. The foregoing tunnel is excavated manually with a one-meter advancing step. In this project, the constructors use a lattice girder and spray concrete with 31 cm thickness as the initial lining. A suitable numerical software for this modeling is PLAXIS 3D Tunnel, which allows high-resolution finite element modeling (FEM) of the studied object. The performance of this method is investigated and compared with that of other NATMs. The numerical modeling yielded a value of 30.01 mm for earth subsidence in the most damaged area of the settlement, which was confirmed with a dramatically low difference by earth surface monitoring. Moreover, this tunnel was drilled and excavated using various methods, among which the least settlement was obtained by the proposed method. The results are promising, and they indicate that tunneling with this method should continue to be used to expand the subway line in the city.

Shear and interface shear fatigue of semi‐precast slabs with lattice girders under cyclic loading

AbstractMore and more often, semi‐precast reinforced concrete slabs with lattice girders are employed for industrial buildings or bridges, where they are exposed to high cycle fatigue loading. Despite research in recent years that has led to the formulation of an S–N curve for lattice girders, the effects of cyclic loading on semi‐precast slabs have not yet been sufficiently clarified. Moreover, research has so far been limited to single‐span slabs. The effects of continuous slab systems, which are mainly realized in buildings and bridges, cannot be considered in the calculation of fatigue resistance yet. To improve the fatigue design concept for shear and interface shear, theoretical and experimental investigations were conducted at the Institute of Structural Concrete, RWTH Aachen University. In addition to the fatigue behavior of 16 tests under cyclic loading, particular attention is paid to the increase in shear and interface shear resistance at the inner support of continuous slabs. Furthermore, the influences of the support detailing were investigated. The findings illustrate further potential for optimization of the design under cyclic loading.

Engineering geological and geotechnical evaluation of Sathya Sai Prasanthi Nilayam railway tunnel, Andhra Pradesh, India

Detailed engineering geological investigations were carried out for a railway tunnel which was constructed more than two decades ago. 3D engineering geological mapping was carried out using Brunton Compass and Total Station Surveying instruments in 1:100 scale. Coarse-grained pink and grey granite, hornblende-biotite gneiss and dolerite dyke of Archaean age and Lower Proterozoic age were mapped. Rock mass was intersected by sub-horizontal, inclined, and vertical joint sets, which were continuous and persistent, smooth, and planar with thick filling of decomposed and crushed sheared material or with thin coating of clay material. Based on the Q-system, rock mass was classified into different classes. On the basis of large-scale engineering geological mapping and Norwegian Method of Tunnelling, a support system was recommended which includes rock bolt, fibre reinforced shotcrete, grouting and reinforced ribs of sprayed concrete and the same is implemented by the agency. As per the best knowledge of the authors, reinforced ribs of sprayed concrete are first time used for transportation tunnels in India and it will be more effective if it will be compared with ISMB or Lattice Girder.

Investigations on Interface Shear-stress Transfer Behavior of Concrete Composite Slabs with Lattice Girders

Investigations on Interface Shear-stress Transfer Behavior of Concrete Composite Slabs with Lattice Girders

Static Bending Mechanical Properties of Prestressed Concrete Composite Slab with Removable Rectangular Steel-Tube Lattice Girders

In recent years, with the development of building technology, the Chinese construction industry has begun to gradually promote the prefabricated buildings to save on construction costs. Among them, composite slabs, as essential components of prefabricated buildings, have been widely used by designers mainly in favor of their low cost. However, is it possible to further reduce the cost without affecting the quality? Researchers think so if the operation cycle of support from the bottom of composite slabs can accelerate and the mechanical properties of their bottom plate can be optimized. To prove this hypothesis, researchers proposed a new type of prestressed concrete composite slab with removable rectangular steel-tube lattice girders (referred to as CDB composite slabs), whose bottom plate consists of a temporary structure composed of a prestressed concrete prefabricated plate and removable rectangular steel-tube lattice girders. Through static bending performance tests on three prefabricated bottom plates and one composite slab, researchers measured corresponding load-displacement curves, load-strain curves, crack development, and distribution, etc. The test results show that the top chord rectangular steel tubes connected to the bottom plate concrete through web reinforcement bars significantly improve the rigidity, crack resistance, and load-bearing capacity of the bottom plate and possess better ductility and out-of-plane stability. The number of supports at the bottom of the bottom plate is effectively reduced, with the maximum unsupported span reaching 4.8 m. Beyond 4.8 m, only one additional support is needed, and the maximum support span can be up to 9.0 m, which provides space for cost reduction. The cooperative load-bearing performance of the prefabricated bottom plate and the post-cast composite layer concrete is good. The top chord rectangular steel tubes are easy to dismantle and can be reused, which reduces the steel consumption by about 24% compared to that used for the same size of ordinary steel-tube lattice-girder concrete composite slabs. It can greatly decrease the cost. In conclusion, the results have shown that the new method researchers proposed here is practically applicable and also provides great space to save on financial costs.

New Approaches to 3D Non-Crimp Fabric Manufacturing

Textile reinforcements have outstanding load-bearing capabilities due to the excellent tensile properties of high performance multifilament yarns (e.g. carbon fibers). However, in order to take full advantage of their high potential, it is necessary to ensure that the filaments run in a straight line. In order to guarantee this straight filament course, the highly efficient multiaxial warp knitting process is used for the production of 2D non-crimp fabrics (NCF) as textile preforms. In various industrial applications, most structures have complex 3D geometries. Therefore, the 2D textile needs to be shaped for reinforcement, which often results in a rearrangement of the filament orientation. Consequently, the 3D shaping process has to be taken into account during the textile production or in the shaping process itself in order to guarantee the highest mechanical properties. Using the example of lattice girders for concrete reinforcement, a new approach for the fabrication of 3D textile lattice girders in a continous shaping process is presented. The results of the production tests of the developed technology approach show no apparent filament damage and exact roving orientation with no inadvertent deflection, compression or bulging, indicating a precise and gentle shaping process. The developed technology contributes to the future reduction of the production costs of 3D textile reinforcements.

Study on mechanical properties of shotcrete lattice girder in a tunnel considering the excavation effect at early-age

The lattice girder (LG) and shotcrete work together to provide support in tunnel engineering, being influenced by the hardening process of concrete and the excavation process. To elucidate the dynamic changes in the mechanical behavior of the LG during this process, the present study conducted indoor experiments using a self-developed loading system suitable for early age flow-plastic state shotcrete LG. Through the secondary development of the ABAQUS concrete hardening process constitutive model, an analysis of parameters such as curvature and load values was conducted to understand the evolution of the load patterns on the LG. Subsequently, relying on the background of the construction of an underground excavation station in Qingdao Metro, refined numerical simulations of the construction process were carried out. Combining the analysis with measured data, the following conclusions were drawn: 1. In the first three days after concrete casting, the LG specimen experiences relatively low stress, and after seven days, the LG specimen and concrete form a cohesive synergy; 2. The initial load caused the deterioration of the supporting performance of the unhardened grid concrete specimens, and the bearing capacity of the test group was reduced by 25% compared with the control group; 3. In the early stages of tunnel excavation and support, due to the low hardening process of shotcrete, the ability to transfer the surrounding rock load to the LG is limited, and the layout of the LG has no significant impact on the stability of the surrounding rock; 4. The collaborative support effect between the rebar bent frame (RBF) and concrete is greater than that of the LG, and it coordinates better with prestressed anchor bolts, presenting advantages in hard rock tunnels.

Common Defects of Prefabricated Prestressed Elements for Industrial Construction

This manuscript attempts to classify typical errors occurring during the design, production, and use of prefabricated and prestressed concrete girders and slabs manufactured in Poland for industrial buildings since the 1950s. Although the cases discussed concern Poland, most of them have a universal character, and as such are also found in other countries. The defects and errors are illustrated with examples and the causes of their occurrence are also discussed. A method of classifying flaws based on the period of their occurrence was proposed. Most of the examples discussed were encountered by the authors during their professional work. In most of the presented cases, repair was possible, enabling further safe operation. This paper shows how important it is to periodically check the technical condition of prestressed structures and how common and at the same time trivial mistakes may be made by designers and contractors of this type of structure, despite the experience of over 70 years of their mass use. The quality of modern prestressed structures is undoubtedly higher. Using the experience of previous generations, designers and contractors abandoned the less durable post-tensioned concrete lattice girders. Errors, if they appear, are most often at the stage of implementing new products or are the result of poor workmanship or disregard for unfavorable weather conditions.

Study on Improved Large Span Propping System for Reinforced Concrete Composite Slabs with Lattice Girders

To further improve the installation efficiency of commonly used reinforced concrete composite slabs with lattice girders in China, an Improved Large Span Propping System is proposed. This article investigates the mechanical properties of the new propping system through in-situ monitoring. The monitoring results show that the displacement and stress of the prefabricated layer can meet the requirements of current Chinese standards, which indicates the feasibility of the new support system. Compared with the original Large Span Propping System, the new propping system can further utilize the bending stiffness of the prefabricated layer and reduce the installation amount of the lower propping frame.

The analysis of variants of the main frame of the two-nave steel hall for sports purposes

The objective of the analysis was the choice of the cross sections of the Steel hall’s main frame. The minimisation of weight of the construction elements was assumed as a criterion of optimisation. Initially, the forces which load the main frame, caused by constant interactions, snów interactions and wind interactions, were calculated. In the first phase of the analysis, the choice of cross sections for the elements of the lattice girder was madę. Ninę variants of the lattice girder were considered and the lightest truss was chosen. In the second phase, the analysis of the cross sections of the spandrel beam and the columns was performed. Four variants of these elements were considered. Similarly to the first phase, the variant considered best in terms of weight of the elements was chosen. The results of the calculations from both phases were shown in the bar graphs

Study on the influence law of cavities behind the shotcrete lining on the lattice girders

The field monitoring data showed that a small amount of main reinforcement bars of lattice girder at the arch of a tunnel were pulled, and the calculation showed that the initial support structure should be compressed. To find out the reason for the tension of the main reinforcement, the geological radar was used to detect the cavity in the sprayed concrete layer at the tension position. In order to clarify the tension mechanism of the main reinforcement and the influence of factors such as the position and size of the cavity on the main reinforcement, numerical simulations were carried out. The results show that the cavity causes the eccentric compression of the shotcrete layer, resulting in moment of the lattice girder and the change of the stress distribution of the main reinforcement. The main reinforcement experiences tensile stress when the cavity size surpasses 3 m × 0.2 m, reaching a tensile stress of 81 MPa at a cavity size of 6 m × 0.2 m. Notably, the cavity located at the foot of the arch is more likely to produce substantial tensile stress on the primary reinforcement compared to those at the arch crown and waist. The research results provide a theoretical basis for the interpretation and analysis of tunnel lattice girder monitoring data.

Mechanical characteristics and stability analysis of an innovative type of steel–concrete composite support in shallow-buried excavation tunnels

Under the influence of the principle of New Austrain Tunnelling Method (NATM), the initial support structure of shallow-buried tunnels in urban soft rock mainly adopts the forms of section steel arches or lattice girder arches combined with bolt-mesh-shotcrete. In order to solve the problems of tunnel deformation and collapse caused by untimely support or insufficient support strength during the construction process, the concept of “timely and high-strength support” was put forward, the high-strength steel pipe grid (HSPG) arch was innovatively designed, and the steel pipe grid bolt-shotcrete (SPGB) structure was established. Next, the flexural bearing performance and failure modes of the joint component and jointless component of the HSPG arch were analyzed, and the design scheme was also optimized by finite element simulation. Then, the full-scale model test of steel pipe grid concrete component (SPGC) under the pure bending load was conducted to explore the coupling bearing effect in a laboratory. In addition, relying on the underground excavation tunnel project of urban subway, the characteristic curves and stability coefficient of surrounding rock and SPGB structure were given by using the principle of convergence-confinement method. Theoretical calculations and on-sit measurements showed that SPGB structure had good adaptability in weak surrounding rock tunnel. In general, the research results were of great significance for clarifying the bearing mechanism and applicable conditions of SPGB structure, and also provided a reference for its further application in the tunnel and underground engineering.

Assessment of the rotational stiffness of single-riveted joints in a steel lattice girder by modal analysis

Wrought-iron and mild-steel riveted lattice girders are widespread structural components of the French metallic construction heritage of 1850–1930. Many rafters and purlins of roof structures of train sheds or market halls are made of flat and angle bars assembled with single-riveted joints. The assessment of the mechanical properties of those joints is key to sensitive and targeted retrofitting operations. Despite its influence on the buckling risk of lattice girders, the out-of-plane rotational stiffness of the joints has not been investigated yet. To fill this gap, experimental and numerical investigations based on modal analysis techniques were carried out on a riveted steel lattice girder dating from 1930. The measured natural frequencies and mode shapes were used to update a finite-element model of the girder. The results suggest that the single-riveted joints exhibit a rigid behaviour in the out-of-plane direction. When numerically varying the rotational joint stiffness, two indicators seem to be relevant, one based on the study of mode shapes, and the other one linked to the presence of additional numerical modes compared to the experimental measurements. Furthermore, a numerical study was conducted to assess the potential use of the findings to develop a modal-based damage detection method for riveted joints. With only one measurement point on each lattice web member, an indicator named ΔECOMAC, derived from the enhanced coordinate modal assurance criterion (ECOMAC) proposed in the literature, appears capable of detecting and localising one or several joints presenting a loss of stiffness. Overall, this paper shows that experimental modal analysis can be an efficient tool for assessing single-riveted joints in old steel lattice girders.

Experimental and Theoretical Research on Welded Aluminium X‐Joints

AbstractAluminium provides many advantages as a construction material in civil engineering, such as for example light weight, functionality by extruded profiles and corrosion resistance. It is obvious to use these advantages also for trusses. However, most aluminium alloys develop zones of weakening due to welding. The so called heat affected zones (HAZ) reduce the load‐bearing capacity of welded aluminium joints by up to 50%. Consequently, the design and execution of welded X‐joints within lattice girders are challenging. Indeed, the design of welded aluminium X‐joints is not specifically treated in EN 1999. Until now, the calculation of aluminium welded X‐joints relies on the steel standard EN 1993‐1‐8, which does not take into account the characteristic of aluminium. This results in errors and inefficient design. Thus, in this experimental research project the behavior of welded X‐joints in real‐scale models is explored. To this purpose, tests have been carried out on lattice girders made from aluminium alloy EN AW 6082 T6. In total, six girders with varying coefficient β and shape of the hollow section of brace members have been investigated. Thereby, the girders were loaded vertically until the failure of the X‐joints. Strains at the brace and chord members were measured by strain gauges and respective stresses were derived. In addition, a comparative analysis between experimentally and theoretically ‐ based on Eurocodes (EN 1993 part 1‐8 and EN 1999 part 1‐1) ‐ obtained results has been made. The analysis shows that the reduction of the load‐bearing capacity of welded aluminium X‐joints due to the HAZ is not constant but varies with the value of coefficient β and the shape of the cross‐section of the brace member. Obviously, the design of welded aluminium X‐joints based on EN 1993‐1‐8 applying a constant value for the HAZ does not reflect the true behavior of these joints as it leads to a quite conservative design approach.

Experimental behavior of lintels for AAC masonry buildings: Comparison among different solutions

AbstractThe paper investigates the experimental behavior up to failure of different types of lintels for AAC masonry buildings. At first, precast highly‐reinforced AAC lintels, that are quite widespread on the European and Turkish market, were tested in flexure, by considering different reinforcement type and arrangement. The second analyzed solution is represented by RC lintels cast within three juxtaposed special AAC elements with U section, acting as formwork and final external finishing. Also in this case, the effect of reinforcement type (lattice girders, ordinary rebars, or a combination of them) and reinforcement amount on the bearing capacity and mode of failure was analyzed. The experimental results highlight that precast AAC lintels available on the market are very light and are characterized by high stiffness in bending; however, being usually over‐reinforced, their failure is quite brittle. On the contrary, RC lintels cast within U‐shaped AAC blocks (“combined AAC‐RC” specimens) are heavier but can be easily designed to have a ductile behavior, by simply following design Standard recommendations for ordinary RC elements.

Development of a highly various warp yarn manipulation system for the fabrication of 2D net-shape non-crimp-fabrics for highly material efficient concrete reinforcements

Textile reinforcements have revolutionized many industries, most of all aerospace, automotive and building. Due to its high performance and the significant increased lightweight potential, they have established themselves as an efficient and sustainable alternative to conventional materials. However, in view of the increasing demand of an ever growing population in contrast to a scarcity of resources and urge of material efficiency in the face of climate change, novel technologies for highly material efficient products in large-scale productions are required. In this regard, a major research field involves the multiaxial warp-knitting technique for the production of high performance textile preforms. In several steps, this technology has been further developed to enable the production of application-specific and bionic-inspired textile preforms, which are characterized by a force compliant and multi-material design. Yet the structural possibilities are still limited. This article presents a novel developed warp yarn manipulation system for multiaxial warp-knitting machines. The system enables the fabrication of 2D net-shape non-crimp-fabrics (NCF) made of up to 16 single warp yarns that specify by an alternating diagonally offset and overlapping edge-strand. This structure is suitable for the use as textile lattice girder for reinforcing concrete slab structures Hereby the developed warp yarn manipulation system allows highly various structural parameters of the 2D net-shape NCF for highest material efficiency and product variety. The technological development is discussed in means of the constructive and electronic control design as well as a specific application example for new net-shape reinforcement structures.

Experimental study on flexural behavior of precast ultra-lightweight ECC plank with lattice girder at construction stage

During the construction of precast concrete (PC) structures, concrete composite slabs are commonly used, employing PC planks with lattice girders as permanent formwork to enhance assembly efficiency while ensuring structural performance. However, traditional PC planks suffer from heavy weight and susceptibility to cracking, adversely affecting construction efficiency and quality. This paper proposes the incorporation of ultra-lightweight engineered cementitious composite (ULECC) into PC planks. The research aims to investigate the flexural behavior of precast ULECC planks with lattice girders during the construction stage. Four-point bending tests were conducted to study the effects of lattice girders and ULECC layer. The introduction of ULECC reduced the self-weight of precast planks by 24%, while resulting in a decrease in strength and stiffness due to ULECC's lower elastic modulus. Remarkably, precast ULECC planks exhibited excellent crack width control. Even at a deflection-span ratio of approximately 4%, precast ULECC planks were capable of maintaining crack widths below 0.2 mm. The combination of ULECC and lattice girders significantly improved the structural performance of precast ULECC planks, allowing them to meet construction requirements without requiring temporary support.

Field Investigation of the Reinforcement and Support Mechanism for a Tunnel in Layered Soft Rock Mass

A crucial deformation phenomenon is observed in shale and silty clay sections in a tunnel. To analyse the reinforcement and support mechanism and behaviour of the tunnel support structure in layered soft rocks, field tests for the axial force of the cartridge rock bolt, surrounding rock pressure, stress of a steel I-beam and lattice girder were performed. Based on the field deformation analysis data, the reinforcement behaviours of the cartridge rock bolt and steel floral pipe, and support behaviours of lattice girder and steel I-beam in the layered rock mass and silty clay were analysed.

Evaluating the Safety and the Effect of Blast Loading on the Shotcrete together with lattice girder Support of Tunnels

Damage to tunnels caused by explosions may damage the support structure and the stability. This damage is due to either blasting the working face for drilling progress or an explosion inside the tunnel. The present study investigates the dynamic parameters resulting from the blasting pattern on the temporary support structure of the tunnel considered as a lattice girder and shotcrete equivalent cross-section. For this purpose, LS-DYNA finite element software was used to assess the dynamic response of the structure to the vibration of the blasting-induced explosion. The peak particle velocity (PPV) was considered to evaluate the safety of the tunnel under dynamic loads. According to the results of this study, by exceeding the velocity of 0.9 m/s in the elements, some levels of destruction will occur. Regarding the elements of the temporary support structure of the tunnel, it is found that the damage occurs near the face and 2 m from the tunnel.