Concrete Encasement Research Articles

Seismic performance of the ST-RC columns to RC beams exterior joint with assembled connection details

An innovative composite column type, the steel tube-reinforced concrete column (ST-RC), consists of a core of concrete-filled steel tube (CFST) and reinforced concrete (RC) encasement. This study aims to validate the reliability of two convenient and rapid assembly methods between RC beams and ST-RC columns. Four full-scale beam-column joint specimens were tested, comprising two prefabricated assembly joints of ST-RC column-RC beam frames, one integrally cast joint of ST-RC column-RC beam frames, and one traditional integrally cast joint of RC column-RC beam frames for comparison. The experiments were conducted based on the principles of a self-balanced system, and quasi-static tests under constant axial compression on the ST-RC columns were performed. Hysteresis curves, skeleton curves, failure modes, strength degradation, energy dissipation capacity, stiffness degradation, deformation capacity and the influence of connection method and joint form on mechanical performance were analyzed and obtained based on the test results. The results indicate that, compared to integral casting, the assembly surrounding method with steel sleeves reduces specimen energy dissipation by 19.8 % and damping ratio by 21 % at 4 % drift, with minimal impact on other mechanical properties. In contrast, reinforcement surrounded and connected by steel plates reduces initial stiffness and peak load-carrying capacity by 1.0 %, along with decreasing negative ductility. It also lowers total energy dissipation by 37.4 % and damping ratio by 45.4 % due to compressive effects from bottom steel plate connections. Despite these effects, its impact on negative ductility and load-carrying capacity remains minimal. Additionally, experimental observations and rebar strain data indicate higher stress on rebars at the base of steel plate connection beams, suggesting a need to strengthen transverse rebars at the beam’s base. The study confirms the feasibility of two convenient and rapid assembly methods for the joints of ST-RC column. Both methods meet current Chinese standards for MCE, with failure modes characterized by “strong columns and weak beams” in both cases.

Bending test of long-span ultra-shallow floor beam (USFB) with two lightweight concretes

This paper presents the bending behaviour of a partially encased ultra-shallow floor beam (USFB) with two types of lightweight concrete. The beam was fabricated by welding two asymmetric Tees together along the web to create a beam with multiple circular openings that act as ‘plug shear connectors’ with the concrete encasement. The bending resistance of the plug-shear connection system was obtained by testing a composite USFB for a beam span of 7.2 m, half of the span being made with a lightweight concrete slab and the other half span with an ultra-lightweight concrete slab. Analysis of the four-point bending tests was carried out to determine the increase in bending resistance due to composite action and the contribution of the longitudinal shear connection due to the concrete plug passing through the web openings combined with additional tie bars. Calculations of the properties of the USFB with the two types of lightweight concrete were made according to SCI documentation and Eurocode 4. It was observed that the deflections were predicted accurately by the elastic properties and that the failure mode was by concrete crushing before the plastic bending resistance of the composite section had been developed. It was also shown that the cracked section properties should be used for the deflection analysis.

Experimental study of ultra-high-performance fibre-reinforced concrete (UHPFRC)-encased CFST short columns under axial and eccentric compression

This study presents a comprehensive experimental programme and analysis of ultra-high-performance fibre-reinforced concrete (UHPFRC)-encased concrete-filled steel tube (CFST) columns subjected to axial and eccentric compression. Twelve short columns were tested, with six of them utilising UHPFRC encasement while the other six employing normal strength fibre-reinforced concrete (FRC) encasement for comparison purpose. The study focused on the effects of load eccentricity ratio, concrete encasement type, and steel tube configuration. Key findings from the test results including failure modes, load-deflection behaviour, moment-curvature relationships and curvature ductility were examined. The findings showed that UHPFRC-encased CFST columns exhibited significantly enhanced strength and bending capacity, while FRC-encased columns showed remarkable ductility. A notable shift in failure mode was observed with increasing load eccentricity ratio, transitioning from crushing of concrete to compression, and then to balanced failure. Furthermore, applicability of prevalent design codes such as EC4, AIJ, and ACI 318 in calculating the peak loads of UHPFRC- and FRC-encased CFST columns was assessed. The plastic stress distribution methods in EC4 and AIJ overestimated peak loads, while ACI 318's strain compatibility approach accurately predicted FRC-encased columns but not UHPFRC-encased columns. To address this, modifications of the parameters α and β were incorporated into the ACI design method to reflect the relative brittle nature of UHPFRC, resulting in accurate predictions.

Study on the Shear Behaviors and Capacity of Double-Sided Concrete-Encased Composite Steel Plate Shear Walls by Experiment and Finite Element Analysis

Concrete-encased composite plate shear walls (C-PSW/CEs) can realize the in-plane shear yielding of infill steel plate with the buckling restrained from the concrete panel. Concrete panels also additionally resist portions of lateral loading in C-PSW/CEs, whereby the shear stiffness and strength of the C-PSW/CE are improved. However, research on the in-plane behaviors of concrete panels and the interactions between structural elements is limited. In this paper, the mechanical characteristics and the interactions and the shear resistances of C-PSW/CEs with double-sided concrete encasements were studied. First, the effects of concrete thickness on the damage process, steel plate buckling, and shear resistances of C-PSW/CEs under lateral loading were tested. Then, finite element analyses of the internal forces of the horizontal and inclined cross-sections and the shear force–drift ratio responses of C-PSW/CEs were undertaken with the extended finite element method (XFEM) to simulate the cracking behaviors of concrete panels. A shear force–drift ratio model based on mechanics was developed by considering the lateral load resistances of concrete panels and their effects on steel plates in C-PSW/CEs.

Axial compression behavior of a prefabricated F4T-section thin concrete encased steel short columns with different stirrup types

A prefabricated F4T-section thin concrete encased steel (F4T-TCES) column with a low reinforcement ratio is proposed to address instability, corrosion resistance issues in pure steel columns, and column protrusion out of the wall. The F4T-section is a T-shaped column with internal steel featuring four flanges. Ten F4T-TCES short columns were tested under axial compression loads, examining five new stirrup types to facilitate construction and study their impact on load-carrying capacity. The effects of steel flange and web thicknesses, stirrup and longitudinal bar diameters, stirrup spacing and form, and concrete encasement thickness on axial compressive behavior were investigated through tests and finite element (FE) analysis. Results indicate that less reinforcement and thin concrete cover can restrain steel elastic buckling and fully utilize material properties. Using 8 mm diameter longitudinal bars and a 1.32 % stirrup ratio provides sufficient strength and adequate confinement. Reliable performance is achieved with a flange thickness of 12 mm, while increasing web thickness beyond 8 mm shows no significant improvement. Increasing concrete encasement thickness from 45 to 70 mm effectively reduces the cracking of the concrete cover. Specimen with stirrup type C exhibits the highest load-carrying capacity, delayed crack initiation, and narrower crack widths, with type D also performing well in crack control. All five stirrup types meet load-carrying requirements, with types C and D being easier to construct and thus preferable. Formulas for the axial compressive strength and a simplified load-axial deformation model for F4T-TCES columns are proposed and validated.

Concrete Encased Grounding: Lightning Response Analysis Considering the Frequency Dependence of Soil

Concrete Encased Grounding: Lightning Response Analysis Considering the Frequency Dependence of Soil

Axial compression behavior of prefabricated cruciform-section thin-concrete-encased steel short column

A novel prefabricated cruciform-section thin-concrete-encased steel (PCS-TCES) column is proposed. Tests were conducted on seven PCS-TCES short columns under axial compression, changing steel section area ratios, concrete cover thickness outside the flange, stirrup spacing and stirrup forms. According to the results, PCS-TCES short columns exhibit excellent axial compressive strength and crack resistance. The stirrup form with welded ends can further improve the crack resistance of the columns. The local buckling of steel sections under axial compression can be prevented by the thin concrete encasement of PCS-TCES columns. With the 45 mm concrete covers outside the flanges that is much thinner than the requirement in the Chinese code, the crack resistance and the deformability of the specimen are still enhanced. The proportion of steel section area in PCS-TCES short columns from 7.4% to 10.8%, although with thin concrete covers, can still fully utilize the strength of the steel and develop considerable residual resistance with satisfactory post-peak deformability. Formulas were proposed and verified to calculate the maximum axial compression resistance of PCS-TCES short columns, and a modification for the elastic stiffness formula in the Chinese code was provided.

Experimental study on exterior precast concrete beam-to-CECFST column joints with wet connections under cyclic loading

Concrete-encased concrete-filled steel tube (CECFST) structural system has gained popularity in recent years due to its several advantages over conventional structures. Additionally, precast technology has become an effective way of improving construction efficiency and environmental performance. Therefore, it is essential to investigate the structural behaviour of precast concrete (PC) beam-to-CECFST column joints to ensure their optimal performance in applications. In this regard, this paper presents an experimental study of 4 precast exterior joints subjected to lateral cyclic loading. The study investigated the effect of replacing normal concrete with steel fibre-reinforced concrete at the joint region and the presence of axial load on PC composite joints. Based on the test results, cyclic load-carrying resistance, failure modes and crack patterns of the PC specimens were recorded and analysed. In addition, a Digital Image Correlation (DIC) system was adopted to show the crack evolution of joint specimens and calculate shear strains of concrete encasement at the joint region. Further comparisons were conducted in terms of ductility, energy dissipation, stiffness and strength degradation to investigate the joint performance. Finally, existing American and European design code provisions were modified and used to predict joint shear strength. Their predictions were reasonably close to the test results.

Mechanical performance of concrete-encased prismatic girders with corrugated steel webs

To enhance the shear buckling resistance of girder bridges with corrugated steel webs (CSWs), especially near the intermediate support where maximum shear force and negative bending moment are experienced, it is common practice to encase the CSWs with concrete. This paper analyses the mechanical performance of concrete-encased prismatic girders with CSWs based on finite element (FE) simulations, theoretical analysis and existing experiments. The concrete encasement restricts the axial free deformation of the concrete-encased CSWs (CCSWs), thereby diminishing the accordion effect of the CSWs. As a result, the normal strains in both the CCSWs and the concrete encasement become nearly identical, demonstrating a linear distribution that aligns with the plane section assumption. The study reveals that the concrete encasement assists the CCSWs in shouldering a portion of the shear force, and shear stress in the CCSWs is no longer uniformly distributed. In addition, a stiffness-based shear carrying calculation method for CCSWs and concrete encasement is theoretically derived. It is observed that due to the constraint of concrete encasement, the actual shear modulus of CCSWs surpasses that of CSWs without encased concrete, rendering it more similar to that of a flat steel plate. Lastly, this study firstly proposes a shear stress calculation formula for CCSWs, which theoretically explains the parabolic shear stress distribution in CCSWs. Error analysis reveals that traditional basic shear method, which assumes uniform shear stress distribution in CSWs, significantly underestimates the actual shear stress in CCSWs. Remarkably, the modified shear method proposed in this study accurately predicts shear stresses in CCSWs.

Renovation of the retention bunker lining on the example of the Mysłowice-Wesoła coal mine

The scientific article focuses on the analysis, renovation and modernization of the retention bunker No. 4 at the 465 m level in the Mysłowice-Wesoła coal mine complex. This bunker, a key part of the mining infrastructure, has an important function in the coal mining process, accumulating output before its further transport to the surface. During a regular inspection of the bunker, significant damage was found in the form of defects on the lining, caused by the impacts of the output flow. Repair efforts required a comprehensive approach, including the use of rope access techniques (industrial mountaineering) for precise damage assessment and repair. The research and repair work included the installation of rappelling stations, rope access rappelling, non-destructive testing, bolting, concrete encasement of the damage, and other innovative repair techniques. Careful adaptation of operations to underground conditions and precise planning of logistics and repair work were key to successfully restoring the bunker’s stability and functionality. An analysis of the renovation process reveals the comprehensiveness of the measures, covering both the north and south sides of the bunker. The use of bolting, steel mesh, and innovative approaches allowed for the successful repair of damage. The ultimate success of the renovation helped minimize the risk of further damage and restore the integrity of the No. 4 retention bunker. The article also highlights the often-downplayed role of bunker in mining infrastructure, arguing that despite having ready-made longwalls and roadways, the absence of a functional bunker makes a coal mining system incomplete.

Axial compressive strength of concrete encased extended T-shaped steel composite columns with less reinforcement

A novel concrete encased extended T-shaped steel composite stub (ET-CES) column with less reinforcement for the prefabricated structure is proposed. Eight ET-CES columns, including one covered by concrete fireproof boards and two bare extended T-shaped steel stub columns, were tested under axial compression. Finite element analysis was also conducted. The effects of stirrup spacing, stirrup form, steel ratio, and concrete compressive strength on the axial compressive behaviour were studied. Furthermore, the failure modes, axial load-displacement curves, axial load-strain curves, and post-peak deformability of ET-CES columns were also investigated. The results demonstrated that the concrete cover with less reinforcement and a thin concrete encasement for the ET-CES column could still prevent steel skeleton instability under axial compression. Premature spalling of concrete cover might be prevented by installing fireproof boards, reducing stirrup spacing, and using closed stirrups. The steel ratio in ET-CES columns increasing from 8.1% to 10.4% had no effect on the maximum normalized resistance but could enhance the post-peak ductility and residual strength. The reduction of the concrete compressive strength of ET-CES columns from C50 to C30 could improve the maximum normalized resistance and residual strength. ET-CES columns had excellent post-peak deformability. Finally, an axial strength formula for ET-CES columns was proposed and validated.

Axial compression behavior of prefabricated T-section thin concrete encased steel short columns

A T-section thin concrete encased steel (T-TCES) column is proposed for the residual buildings, avoiding the convex corners in rooms. The required concrete cover thickness for concrete encased steel members specified in the existing codes is quite large, which is the key problem and to be solved in the proposed column by reducing the concrete covers, facilitating the transportation and installation. To evaluate the mechanical performances of the proposed columns, especially the local stability of the internal T-section steel with the obviously reduced concrete covers, tests of nine short column specimens were conducted under axial monotonic loading. Also, the finite element (FE) analysis was conducted and validated. The effect of the proportion of steel sectional area, concrete strength, stirrup spacing and the concrete encasement thickness outside the flange on the failure modes, load-displacement responses, load-strain responses and characteristic loads were obtained. According to the test and FE analysis results, the peak load can be improve by increasing concrete strength or the proportion of steel sectional area or decreasing the stirrup spacing. The T-TCES columns with low-grade concrete or small stirrup spacing or high proportion of steel sectional area have a better composite action between the internal steel and concrete. Increasing the thickness of the concrete encasement outside the flange can prevent the T-TCES column from cracking. The concrete encasement and reinforcement bars can restrain the internal steel buckling, and improve the steel strength of the composite column compared with the steel column. The calculation methods for the peak and design resistances of the T-TCES column were proposed and proved to show satisfactory accuracy. The simplified model of the load-displacement responses and the calculation methods of the axial stiffness are proposed and validated against the test results.

Investigation of the Buckling Capacity of Concrete Encased Steel H-Piles on Highway Bridge Structures

Investigation of the Buckling Capacity of Concrete Encased Steel H-Piles on Highway Bridge Structures

Rehabilitation of Corroded Steel Bridge Girder Ends using Partial-Height Ultra-High-Performance Concrete Encasement

Beam end corrosion is one of the most prominent types of deterioration on simple-span steel bridges. To address this concern, the Connecticut Department of Transportation and the University of Connecticut have jointly developed a repair method for corroded steel girder ends using ultra-high-performance concrete (UHPC) encasement. In this repair, shear studs are welded to the undamaged portion of the web and encased in UHPC to create an alternate load path for bearing and shear forces. This novel repair method has been implemented in multiple states. The widespread promotion of steel girder end repair with UHPC demonstrates the need for literature on field implementations and alternative designs. This paper advances the findings from a field implementation completed in Connecticut in October 2021, which was the first instance of a partial-height repair in the country, the first application of the repair to a weathering steel bridge, and the first use of flange studs to restore shear capacity at the junction of the web and bottom flange. Two of the girder ends were fully instrumented to collect data on the performance of the repaired locations. The paper presents an overview of the bridge, discusses the design and implementation of the repair, provides short-term monitoring data showing its successful activation, and discusses lessons learned throughout the process. It is anticipated that the findings put forward provide support for the use of UHPC encasement as a promising method for the repair of corroded steel girder ends.

A comparative study on steel‐concrete composite columns for use in RC Tall Buildings in Seismic Areas

AbstractUsable/rentable floor areas are crucial for the building owners in reinforced concrete (RC) tall buildings. To address this issue, concrete‐encased (CE) or concrete‐filled (CF) composite columns are proposed as alternative vertical load carrying elements by providing the required strength and ductility, but with smaller dimensions. Comparing the performance of columns with different configurations can be done using moment (M)‐axial load (N) interaction curves. This paper summarizes the approaches proposed by Eurocode 4 and AISC 360‐16 for both types of composite columns, presenting simplified and true curves for a specific class of sections. Two case studies involving hybrid RC tall buildings in Istanbul, which utilized composite columns, are presented along with a comparison with steel‐concrete composite and RC solutions. Numerical results indicate that employing steel‐concrete composite columns resulted in approximately 24% reduction in total cross‐sectional areas for one of the case studies, leading to increased usable/rentable areas. Additionally, concrete‐encased and concrete‐filled composite columns exhibited similar performance in terms of axial load‐moment capacities. The impact of longitudinal rebar ratios is also investigated, revealing that the AISC 360‐16 approach yields smaller bending moments and compression capacities compared to Eurocode 4 due to the significant strength reduction factor considered in calculating the concrete contribution in composite sections.

Experimental and Numerical Investigations of Laced Built-Up Lightweight Concrete Encased Columns Subjected to Cyclic Axial Load

The steel-concrete composite column comprises a steel core and surrounding concrete. The purpose of the system is to provide analysis and design techniques for a newly invented class of laced steel-concrete composite short columns for cyclic axial loads. To minimize the increasing density issues associated with nominal strength concrete and in consideration of the depletion of natural resources required to produce concrete, factory-obtained lightweight sintered fly ash aggregates with and without basalt fiber are employed. The normal-weight concrete containing basalt fiber is shown to be more ductile than any other column. The axial deformation of columns LNA and LSA at failure was found to be 3.5 mm, whereas columns LNAF and LSAF reached an axial shortening of 4.5 mm at failure. The column LSAF was found to have 5.3% more energy absorption than the LSA and 11.5% less than the column LNAF. It was observed that the rigidity of these fabricated components had been enhanced. It was found that the section configuration with a lacing system had improved confinement effects and ductility. Comparing the finite element analysis to the experimental data revealed a strong connection with numerical modeling, with a variance of around 8.77%.

Axial compression behavior of prefabricated L-section thin concrete encased steel short columns

A prefabricated L-section thin concrete encased steel (L-TCES) column, which could be prefabricated in shop, connected on site, and not convex out of wall, was proposed. Changing the proportion of steel sectional area, concrete strength, stirrup spacing and the concrete encasement thickness outside the flange, experimental and numerical investigations were conducted on the axial compression performances of the proposed composite column, and the failure modes, load-displacement curves, load-strain curves and characteristic resistances were analyzed. According to the results, the concrete encasements and reinforcements can restrain the steel buckling, and increasing the proportion of steel sectional area or the concrete strength can improve the ultimate resistance and stiffness of the column. Increasing the thickness of concrete encasement outside the flange could prevent the concrete from cracking, and compared with steel column, the resistance of steel in the composite column can be more fully utilized under the ultimate load. The formulas to calculate the design and ultimate resistance for the composite column with closed stirrup were proposed, providing results with satisfactory accuracy. The simplified model of load-displacement curve was proposed and validated against the test results.

Composite Cold-Formed Steel Beams with Diagonal Rebars for Earthquake-Resistant Buildings.

The construction industry is on the lookout for cost-effective structural members that are also environmentally friendly. Built-up cold-formed steel (CFS) sections with minimal thickness can be used to make beams at a lower cost. Plate buckling in CFS beams with thin webs can be avoided by using thick webs, adding stiffeners, or strengthening the web with diagonal rebars. When CFS beams are designed to carry heavy loads, their depth logically increases, resulting in an increase in building floor height. The experimental and numerical investigation of CFS composite beams reinforced with diagonal web rebars is presented in this paper. A total of twelve built-up CFS beams were used for testing, with the first six designed without web encasement and the remaining six designed with web encasement. The first six were constructed with diagonal rebars in the shear and flexure zones, while the other two with diagonal rebars in the shear zone, and the last two without diagonal rebars. The next set of six beams was constructed in the same manner, but with a concrete encasement of the web, and all the beams were then tested. Fly ash, a pozzolanic waste byproduct of thermal power plants, was used as a 40% replacement for cement in making the test specimens. CFS beam failure characteristics, load-deflection behavior, ductility, load-strain relationship, moment-curvature relationship, and lateral stiffness were all investigated. The results of the experimental tests and the nonlinear finite element analysis performed in ANSYS software were found to be in good agreement. It was discovered that CFS beams with fly ash concrete encased webs have twice the moment resisting capacity of plain CFS beams, resulting in a reduction in building floor height. The results also confirmed that the composite CFS beams have high ductility, making them a reliable choice for earthquake-resistant structures.

Evaluation of hybrid NSM-CFRP technical bars and FRP sheets for seismic rehabilitation of a concrete bridge pier

Seismic retrofit is a cost-effective and sustainable solution for improving bridge structures in seismic zones. Fiber Reinforced Polymer (FRP) is commonly used to replace steel components in retrofit projects due to their light weight, high strength, and high corrosion resistance. The fabrication of novel hybrid structures from FRP and concrete is the next step researchers are addressing. In this context, the present study focuses on numerical modeling of the experimentally determined response of a hybrid FRP and concrete bridge pier subjected to quasi-static tests. The results from FEM showed strong agreement with the experimental response in terms of load-displacement curve and failure mode. After validating the model, alternative designs (changing the height of the CFRP slab, changing the height and compaction of the CFRP bar, and concrete encasement with and without CFRP slab) were numerically tested to investigate the effects of each model on the load capacity. With the conventional concrete encasement, the bearing capacity of the bridge pier can be rehabilitated, but with the CFRP plate in the above system, the bearing capacity of the bridge pier is increased by more than 60%. Therefore, it can be concluded that seismic strengthening techniques with CFRP sheets and mounted NSM-CFRP bars are suitable for concrete bridge piers.

Seismic Behavior of 3D Joint between Concrete Encased Steel Cross-Shaped Column and Steel Beam: Experimental Study

Seismic Behavior of 3D Joint between Concrete Encased Steel Cross-Shaped Column and Steel Beam: Experimental Study