Concrete Segments Research Articles

Effects of warping shear deformation on the torsional load-bearing behaviour of assembled half-shell structures for wind energy towers

This paper deals with an extended analytical calculation model for the torsional load-bearing behaviour of assembled half-shell structures. The objective is to transfer the complex torsional load-bearing behaviour of segmented tower constructions into a simplified and mechanically comprehensible bar model. The presented approach determines the proportional load-bearing effects of shear force and torsion of a cut out single half-shell for a global torsional load based on the deformation equilibrium. The previous model approach – including the principle of load redistribution and the flexibility method – leads to a slenderness-independent determination of the load-bearing components. The developed method enables the specific isolation of the geometric influencing variables by separating the deformation-depending partial internal forces. In addition, the deformation approach can be used to investigate the influence of warping shear softness on the load-bearing behaviour of compact reinforced concrete segments with vertical joints according to the extended warping theory. Compared to the extended first-order warping torsion, the significantly simplified deformation calculation based on the second-order tension rod analogy leads to sufficiently accurate results. In general, the internal force calculation is considered to be extremely sensitive to the smallest changes, so that the improved and much more accurate approach finds its application. The numerical validation leads to very good matches of the internal forces as well as the deformations and stresses.

3D numerical investigation on response of shield tunnel under combined effects of fire and structural loading

As a significant infrastructure hazard, fires in tunnels have brought about a great deal of economic and social losses each year. From a holistic tunneling design perspective, it is essential to predict accurately the displacements and internal forces of the lining under coupled effects of elevated temperatures and various loading conditions. To this end, an elaborate three-dimensional (3D) numerical model, which incorporated the concrete segments, reinforcing rebars and connecting bolts, was established to investigate the deformation and failure mechanism of the segmental ring in shield tunnels under coupled effects of fire and structural loading. The validation based on the experimental results of segment lining and joints shows that the established model can be employed to analyze the entire tunnel ring structures. Two types of numerical models, i.e., single-ring and three-ring models, were established and the thermo-mechanical coupled performance were examined. Based on the verified model, the general temperature field and deformation distribution were described and elaborated. With respect to the significant insights on mechanical behaviors of shield tunnel rings in fire, the results of inner force redistribution, the joint opening elaboration and the failure mechanism of the shield tunnel structure under fire effects and initial loadings were further discussed. The results of this study can provide valuable guidance for the fire resistance design in the tunnel.

Thermal performance and parameter study of steel fiber-reinforced concrete segment lining in energy subway tunnels

This study proposes an effective approach for improving the energy performance of subway tunnels by using steel fiber-reinforced concrete (SFRC) segments to obtain shallow geothermal energy. Three-dimensional time-dependent thermohydraulic finite element analyses of the subway tunnel lining with reference to the existing Shenzhen subway tunnels were conducted. The width of each pipe segment is 1.5 m and a tunnel lining-ground model with size of 25 m × 25 m × 3 m was studied. The influencing factors including the inlet temperature, flow velocity, operation mode, pipe arrangement, and thermophysical parameters of SFRC were considered in evaluating the heat transfer performance of the tunnel lining. The results confirm that the heat-exchange performance of the SFRC segment is noticeably better than that of the ordinary concrete segment. Also, there is a linear relationship between the thermophysical parameters and the heat exchange per unit length. Heat exchange increased with an increase in flow rate until a certain level and became stabilised. Based on the thermal results and economical considerations, the inlet fluid velocity around 0.6 m/s is recommended. Besides, the heat exchange tube spacing between 0.5 m and 0.7 m can ensure both the heat exchange per unit length of the heat exchange tube and the heat extraction per unit tube sheet inner surface area to have high values at the same time. In terms of heat exchange, the advantages are more obvious for cooling operation than heating operation. The heat exchange per unit segment area of the energy tunnel increased with the inner diameter of the embedded pipes. However, the relationship between the rate of heat exchange increase and the pipe spacing changed with the thermal conductivity of the concrete segment.

Moisture-resilient performance of concrete basement walls – Numerical simulations of the effect of outward drying

The moisture safety designs of basements used for habitation have become a topic of concern. Basements are prone to high moisture strain and have a limited outward drying ability compared with above-grade structures. The risk of interior moisture-related damage can be reduced if the basement walls are allowed to dry outward below grade. The use of vapour-permeable thermal insulation and the effect of air gaps behind dimpled membranes on the outward drying of concrete basement walls were investigated in this study. One- and two-dimensional hygrothermal simulations were conducted using WUFI®Pro and COMSOL Multiphysics®. First, the outward drying of concrete wall segments, previously investigated in a laboratory experiment, was simulated. Two EPS types and two dimpled membrane positions were compared, with an emphasis on the airflow through the air gap behind the membrane. Second, the long-term moisture performance of concrete basement walls was simulated. It was observed that when the dimpled membrane was placed between the concrete and exterior EPS, the bottom of the concrete segments dried faster than the top. When the dimpled membrane was placed on the exterior side, the concrete dried more uniformly along the height. Thus, the results indicated that the latter ensured outward drying of the concrete basement walls. However, the overall effect on the interior RH depended on the characteristics of concrete and the amount of interior and exterior insulation. Optimum drying was achieved when the thickness of interior insulation was reduced. The variability of the concrete properties used in basement walls requires further investigation.

Reducing Thermal Crack Risks Caused by Restraint in Young Concrete - A Case Study on Walls of Water Tanks

Abstract Concrete cracks in structures such as water tanks and nuclear power stations cause anxiety to owners, contractors and engineers. These cracks may significantly increase the structure’s permeability and thus increase leakage, reduce durability, and eventually lead to loss of structural functionality. Therefore it is important to minimize their occurrence and size. To identify effective ways of minimizing cracking in young concrete segments, a parametric study was conducted using the finite element method (FEM). Parameters considered include casting sequence, joint position, wall height, and cooling. The study examined continuous and jumped casting approaches to the casting of a cylindrical reinforced concrete tank for a sewage-treatment plant, with and without the application of the ‘kicker’ technique in which the lower part of the wall is cast with the slab. The main cause of cracking is thermal change and restraint imposed by adjacent older structures, and the FEM predictions agree well with experimental observations. Continuous casting is most effective at minimizing cracking because it creates only two contact edges between newly cast and existing structures producing the lowest level of restraint. The kicker technique is shown to be very effective for reducing restraint and consider rephasing.

Numerical analysis of tunnel segments strengthened by steel–concrete composites

In order to study the feasibility of strengthening of segmental tunnel linings by using steel–concrete composites (SCC), a three-dimensional (3D) finite element (FE) model is proposed in this paper. The nonlinear mechanical behavior of concrete is described by a plastic-damage model. The nonlinearity, resulting from the interface of the SCC and reinforced concrete (RC) segments, is simulated with the help of a system of springs. The analysis results are compared with those obtained from a full-scale test of a tunnel segment. Their agreement validates the usefulness of the 3D FE model. Numerical re-analysis of the test shows that the interfacial connectors govern both the strengthening effect of SCC and the failure pattern of the strengthened segments. Thus, the force-transmitting capacity of the interfacial connectors should be concerned in design activities. As regards the circular segments, the interfacial connectors refer to both the shearing and the stripping connectors. The composite effect of the SCC and RC segments increases with the increasing number of these connectors. The latter, therefore, results in the increases of the bearing capacities and stiffnesses of the strengthened segments. Those increases become insignificant as the number of these connectors is sufficient to ensure a perfect composite effect of the SCC and RC segments. In addition, the numerical simulations show that using high-performance steel shell (HPS) or/and ultra-high-performance concrete (UHPC) is an effective way to increase the strengthening effect of SCCs.

Brief Analysis of Safety Management of Precast Concrete Segment Production in TBM Tunnel

Brief Analysis of Safety Management of Precast Concrete Segment Production in TBM Tunnel

Numerical and analytical studies of flexural behaviour of prestressed UHPC joints

This study numerically and analytically investigates flexural behaviour of precast ultrahigh performance concrete (UHPC) segments connected by post-tensioned prestressing strands with or without epoxy on keyed joint surfaces. The analytical formulas are proposed for calculation of joint opening load and ultimate flexural capacity, and a numerical model is established to investigate flexural behaviour of the jointed beam. The joint surfaces without epoxy are simulated by a pair of contact elements with a friction coefficient of 0.6. For the joint surfaces with epoxy, besides the contact elements, a spring element is defined for consideration of the epoxy and an optimized force–displacement relationship is first proposed and input for the spring property. The previous test data and data from one intact beam with low reinforcement ratio tested in the present study are used for validation of the analytical and numerical calculations. The numerical results agree well with the test results in terms of load-midspan deflection, load-joint opening displacement as well as failure modes. Based on the validated numerical model, the effect of number of prestressing strands and beam depth on the flexural behaviour of the prestressed jointed beam is investigated. This study will promote prestressed UHPC joints’ application in practical engineering.

“Concrete Soldiers”: T-walls and Coercive Landscaping in Iraq

Standing inside a t-wall factory in Erbil in the summer of 2021, I was struck by the fact that, nearly twenty years after the US invasion of Iraq, these military walls were still in production. T-walls are six-ton steel-reinforced, blast-proof concrete wall segments named for their upside-down t-shape (Fig. 1). They were introduced to Afghanistan and Iraq in the early 2000s. Derivative of the Berlin wall's design, they are recognizable to those who have witnessed the Israeli separation wall, which is composed of thousands of t-walls lined up.

Numerical modeling of the fire behavior of reinforced concrete tunnel slabs during heating and cooling

This paper examines different modeling approaches to simulate the behavior of reinforced concrete (RC) tunnel slabs under fire during both the heating and cooling phases. Three modeling strategies are investigated by using beam, shell, and solid elements in addition to different methods to capture the effect of axial restraint on the slabs. The models consider temperature-induced plastic deformations and irrecoverable degradation of materials. The models also utilize distinct concrete properties for heating and cooling as well as account for the transient creep strain explicitly in the calculations. The results obtained from different modeling strategies are compared to five recent fire tests on loaded and restrained large-scale RC tunnel slabs, with varying concrete strengths, restraint levels, and fire scenarios. Temperature and displacement evolutions during heating and cooling obtained from the numerical models are compared with the experimental test data. When considering model accuracy and efficiency as the primary performance metrics, using shell elements to analyze the fire performance of reinforced concrete tunnel segments resulted in the best balance between the two. The numerical models and techniques developed in this paper will enable practicing engineers to reliably and rapidly assess fire damage to reinforced concrete tunnel linings, and to explore cost-effective designs of tunnels for fire.

Deformation recoverability of longitudinal joints in segmental tunnel linings: An experimental study

The shield-driven tunnel is a fabricated lining structure. The existence of longitudinal joints between segments in a ring makes the entire tunnel lining vulnerable to deformations, because the rigidity of longitudinal joints is lower than that of the main concrete segments. Large transverse deformation, accompanied by joint opening, is a common disease of shield tunnels. The aim of this work is to explore the deformational behaviors and mechanical properties of tunnel longitudinal joints under overloading, unloading, and soil grouting conditions, with emphasis on the recoverability of joint deformation. For this purpose, a series of laboratory tests have been carried out on the full-scale longitudinal joints at tunnel crown adopted in Shanghai metro tunnels, including three parallel tests with different overload levels and one cyclic overloading and unloading test. The full-scale testing considers the actual stress state of the longitudinal joint under different working conditions in real environments. The specimen of the longitudinal joint at tunnel crown adopts the actual three-segment-two-oblique-seam structure, which is different from the simplified two-segment-one-straight-seam form used in previous studies. Multiple deformation indicators, including joint opening, concrete strain, and bolt strain, are monitored and analyzed. Based on the test results, the effects of restoration actions, i.e., unloading and soil grouting, on joint deformation recovery under different overload levels are discussed. The change of recovery efficiency with the degree of joint deformation is also obtained. In addition, the deformation recoverability and rotational stiffness are compared between the longitudinal joint at tunnel crown which is subjected to positive bending moment and the longitudinal joint at tunnel springline which is subjected to negative bending moment. The test results show that the larger the joint deformation caused by overload, the lower the recovery efficiency. From a mechanical perspective, soil grouting is an effective measure to recover the large deformation of shield tunnels.

Experimental study on the joint bearing behavior of segmented tower structures subjected to normal and bending shear loads

AbstractThis article deals with the analysis and evaluation of the structural behavior of segmented tower constructions in large‐scale experimental investigations. For this purpose, a tower model with dry horizontal joints on a scale of approximately 1:10 is constructed and loaded. The objective of these large‐scale investigations is to determine the load‐bearing behavior of concrete segment towers subjected to normal force (external prestressing), bending, shear force and torsion and to derive more efficient and realistic design models. The transfer of shear stresses between individual segments is ensured by frictional resistance in the horizontal joints due to prestressing. The current design models are based on plane flange surfaces at the top and bottom of the segments as well as their ideal circular ring shape. This assumes a constant normal stress distribution for the compression connection. Within the large‐scale experimental tests, findings for uneven force distribution in the horizontal joints due to prestressing and shear bending were obtained, that have a significant impact on the design models. However, for the evaluation of the results and the projection onto the real construction components, the scale effects must be urgently taken into account.

Temperatures and gradients in concrete Bridges: Experimental, finite element analysis and design

Aiming to introduce a simplified flexible design model for thermal actions in concrete bridge superstructures, experimental and finite element works were carried out in this study. From an experimental concrete box-girder segment, concrete temperature, solar radiation, air temperature and wind speed records for a complete one-year cycle were recorded and utilized. In addition, a thermal finite element model was conducted and verified, which was then used to conduct required parametric studies. Finally, the verified finite element model was used together with long-term climate history (from 1960 to 2013) of 10 cities in Turkey to propose the thermal actions' design models and procedure. Both positive and negative vertical temperature gradient models were introduced in terms of the top surface maximum temperature gradient, which is related to the solar radiation history of the region. In addition, simplified correlations and design procedure were suggested to evaluate the maximum and minimum mean temperatures of concrete bridges using the long-term maximum and minimum air temperatures.

Reliability based optimization of steel-fibre segmental tunnel linings subjected to thrust jack loadings

The circular lining in mechanized tunnelling consists of concrete segments, which are exposed to different loading cases during tunnel construction. One of the most critical loading condition is the thrust jack force, which is induced to the lining segments by the Tunnel Boring Machine (TBM) during construction. Experimental campaigns showed that steel fibre reinforced concrete is suitable for bearing such loads and could replace conventional reinforcement schemes. In this contribution, a numerical model is presented, which allows to directly track the influence of important design parameters such as fibre type, fibre orientation, fibre content and concrete strength on the structural response of steel-fibre reinforced segments. For this purpose, submodels on the single fibre level are combined into a crack bridging model considering the fibre orientation and the fibre content. The submodels are integrated into a finite element model to perform numerical structural analyses. Two validation examples demonstrate that the modelling approach is capable to predict the failure loads as well as the crack development of fibre reinforced specimens subjected to localized loads. Finally, an optimization procedure is carried out to determine a robust and cost-effective design of a fibre reinforced segmental linings. A hybrid reinforcement scheme consisting of two layers of fibre reinforced concrete is employed in order to provide an improved material utilization. The thickness of the segment and the fibre content are optimized taking uncertainties of the material parameters and construction tolerances as uncertain a priori parameters into account. A sufficient load bearing capacity and serviceability performance under all possible conditions is ensured by the consideration of accepted failure probabilities as constraints in the optimization task.

Retrofitting techniques of damaged concrete structure for environment concern: A review

Initiation and progression of damages in the concrete systems is the cause of reduction of structural strength and its durability. The significant retrofitting strategies are required to improve the damages and thus, the performance of infrastructures can be enhanced. The damages in the concrete system is due to several factors viz., ingress of alkaline water, wet-dry cycle, sulfate attack, thermal changes, chloride penetration, and freeze–thaw cycle etc. Changes in the shape and size of concrete segments before and after retrofitting decreases the strength of structural systems and consequently, reduced the durability of retrofitted materials. This review paper is motivated on the application of the retrofitting techniques using Fiber Reinforced Polymer (FRP) material for environment concerned. The deterioration of concrete structure and FRP retrofitted materials durability were discussed. The durability aspect of damaged concrete structure retrofitted with FRP materials under alkaline water, wet-dry cycle, freeze–thaw cycle, open cracks, and water immersion were reviewed. The de-bonding of FRP materials have been described to improve the structural integrity. The suitability of various retrofitting techniques were covered. This paper have been included the retrofitting techniques for the improvement of infrastructural facilities and further, the cracks filled rich cement mortar with FRP over that was the key finding. The review paper will facilitate innovative research directions to the industrialist and researchers.

Three-dimensional numerical study of the reactive powder concrete segments in tunnel lining

Abstract The tunnel lining systems act as lines of defence against the forces and geotechnical situations. The use of precast concrete tunnel linings (PCTLs) has been escalating due to its effective and economical installation process. The tunnels usually suffer from the premature deterioration due to corrosion of the reinforcement and thus need maintenance. Corrosion leads to the distress in PCTL leading to the cracking and finally the scaling of concrete. This study aims to assess the structural durability performance of reactive powder concrete (RPC) as the material of tunnel lining segments compared to reinforced concrete (RC) and high performance concrete (HPC). The numerical findings indicated that the maximum load capacity of PRC-PCTL segments was greater than that of the corresponding RC and HPC segments. Regarding the findings, PRC is a very significant option for conventional segments. The high strength of PRC can decrease the thickness of the PCTL segments, resulting in the decreased material cost. Also, PRC-PCTL segments can eliminate the laborious and costly production of RC segments and mitigate the corrosion damage and thus enhance the service life of lining segments.

Rehabilitation of Defective Connections between Two Precast Concrete Segments (Experimental and Analytical Study)

Rehabilitation of Defective Connections between Two Precast Concrete Segments (Experimental and Analytical Study)

Experimental Study on the Axial Compression Performance of an Underwater Concrete Pier Strengthened by Self-Stressed Anti-Washout Concrete and Segments.

Compared with the conventional drainage strengthening techniques, the precast concrete segment assembly strengthening method (PCSAM) is regarded as a fast, more economical, and traffic-friendly underwater strengthening method for damaged bridge piers and piles, as the drainage procedure can be omitted. However, this method still has some disadvantages, such as strength loss of the filling material, debonding of the interface due to shrinkage of the filling material, poor connection effects, and poor durability of the segment sleeves. To solve these problems, the PCSAM is improved in this study by using self-stressed anti-washout concrete (SSAWC) as the filling material and by developing a lining concrete segment sleeve (LCSS) by referring to the design theory for shield lining segments. Six specimens are designed and prepared with consideration of the influential factors, such as the self-stress, thickness of the filled concrete, and concrete strength of the LCSS, then the monotonic axial compression test is carried out to investigate the improvements in the axial compression properties of the specimens. Accordingly, extended parametric analyses are performed based on the established numerical models. Finally, the calculation formula for the bearing capacity is proposed based on the analysis results. The results indicate that the SSAWC can provide initial confining compressive stress in the core region of the piers, in addition to increasing the bearing capacity and ductility of the specimens. The improved LCSS segment connection is more reliable and increases the strengthening efficiency. The influence of self-stress on the bearing capacity of the specimens is cubic and the influence of the filled concrete strength on the bearing capacity of the specimens is nonlinear. The calculation formula for predicting the bearing capacity of axially compressed columns possesses good applicability and can be used as a reference for practical engineering.

Segmental Intelligent Model Test of Box Girder Bridge Strengthened By a Cable-Stayed System by Mathematical Calculation

Dongming Yellow River Highway Bridge is an important super large bridge across the Yellow River on national highway 106. In order to effectively improve the cracking and deflection of the bridge, the cable-stayed system is used to reinforce the main girder of the project. In order to analyze the stress state of joist, bracket and box girder, the static loading of cable is carried out through scale model test to study the mechanical properties of concrete box girder segment, joist and bracket, verify the reliability of bracket and concrete box girder anchorage, and optimize the reinforcement method of cable-stayed system according to the test results.

Optimization of Bolted Connection in Steel Corbel Attach to RC Column of MRT Viaduct

MRT is one of the backbones of a city’s public transportation system, capable of carrying large crowds. The use of a portal frame in the design of an MRT train station has raised significant concerns about how the portal frame’s load will be supported by the extended structure element known as a corbel. A corbel is a protruding structural element that supports weights like primary beams and girders. Engineers must then decide how to properly bolt the steel corbel structure to the concrete pier segment or columns. Generally, most corbel structure designs were constructed of concrete; however, in this study corbel design was made of steel so that the steel portal frame could rest on the corbel structure, allowing for more usable area on the platform, such as kiosks and other amenities. Optimization of end plate thickness and beam web thickness is carried out. Manual calculations are used in addition to FEA modeling to examine the bolt’s deflection, shear, bearing, tension, slip, and block tearing resistance. When using Eurocode, all three loadings, transverse force, vertical force, and transverse moment, produce values that are 10% lower than the British Standard. As a result, designers can optimize their designs using Eurocode.