Steel Hoops Research Articles

Experimental Evaluation of Seismically and Non-Seismically Detailed External RC Beam-Column Joints

An experimental investigation was undertaken to study the seismic performance of external reinforced concrete (RC) beam-column joints having representative details for mid-rise RC frame buildings in developing countries such as Iran that were designed and constructed prior to the 1970s. Three half-scale external RC beam-column joints were tested by applying lateral cyclic loading of increasing amplitudes. Tested specimens were comprised of one unit having seismic reinforcement detailing in accordance with the seismic requirements of ACI 318-11, and two units having non-seismic reinforcement detailing in accordance with the 1970s construction practice in many developing countries, such as Iran. Two typical defects were considered for the non-seismic units, being the absence of transverse steel hoops and insufficient bond capacity of beam bottom reinforcing bars in the joint region. Test results indicated that the non-seismically detailed specimens had a high rate of strength and stiffness degradation when compared to the seismically detailed specimen, which was attributed primarily to the joint shear failure or bond failure of the beam bottom bars. The non-seismically detailed specimens also showed a 30% reduction in both average strength and ductility and a 60% loss of energy dissipation capacity in comparison to the seismically detailed specimen.

Experimental Tests of Historic Bent Timber Elements Reinforced with Steel Hoop and Mortise-Tendon Joint

The paper presents the results of studies proposing to use steel hoop and mortise-tendon joint (SHMT), to reinforce beams with defects (biological corrosion, cracks) in order to restore their load-bearing capacity. The proposed solution, consisting in encapsulated or bonding steel tube outside of the damaged part, is suitable for restoration work in historic buildings. Moreover, owing to the fact that the reinforcing steel tubes are situated outside the lap joint , the possibility that the crack of reinforcing joint will reduced and the fire resistance of the element is increased. The displacement loading control method was adopted in bending test. The restoration in the load-bearing capacity of the tested beams amounted from 4.42% to over 44.52%.

Cyclic Behavior of Reinforced Concrete Beams with Corroded Transverse Steel Reinforcement

This study examined the seismic performance of reinforced concrete beams with corrosion only induced in the transverse steel reinforcement by using cyclic loading. The beams were designed with closely spaced steel hoops as transverse reinforcement conforming to the seismic design provisions of the ACI 318 code. Seven beams were constructed. One beam was used as a control without corrosion. The other six beams were subjected to six levels of corrosion in the potential plastic hinge region by using an electrochemical method. Corrosion test results indicated that pitting corrosion increased with an increasing corrosion level. The hoops fractured at a corrosion weight loss of 35%. Cyclic test results indicated that the beams could sustain a corrosion weight loss of 6% in the hoops and still maintain ductile flexural behavior. The corrosion of hoops adversely affected the deformation capacity of the beams significantly, yet did not significantly influence the load-carrying capacity of the beams. The residual shear strength provided by concrete and steel was still sufficient to develop flexural yielding, even for beams with hoops corroded to fracture. Methods were developed to estimate the residual shear strength and ductility of reinforced concrete beams with corroded hoops. The amount of corrosion substances filled in the cracks’ volume was approximately 25% of the reduced volume of steel due to corrosion. Although shear strength estimation based on the average corrosion weight loss was not conservative, the shear strength estimation based on the minimum residual cross-sectional area was too conservative at a high corrosion level due to severe pitting corrosion. Shear strength estimation based on average weight loss and minimum residual cross-sectional area produced results that describe the experimental behavior more reasonably.

History-Based Assessment of the Dome of the Basilica of S. Maria of Carignano in Genoa

This article discusses the assessment of the dome of the Basilica of S. Maria of Carignano in Genoa, designed by Galeazzo Alessi in the 16th century. The access to the private archive of the Sauli Family allowed a detailed history of the Basilica to be reconstructed clarifying several crucial aspects of the structure: the actual depth of the foundation system, the materials of the load bearing structure, mainly of the dome and of the drum, and the actual building sequence. The restoration works (steel hoop) carried out in the past decades, discovered by means of the historical research, are related to the severe crack pattern of the dome, which today necessitates a detailed insight into its mechanical response. It is showed that historical information is the key for understanding several issues that a “technological” engineering approach would leave unsolved. In addition, historical data are used to setup a non-linear incremental finite element model (FEM) procedure, referred to a slice (a ratio of 1/16) of the structure due to symmetry conditions, which is able, in spite of its reduced computational demand, to show that the dome response is strictly related also to the drum features, thus explaining cracking and the role of hooping stresses (and ties) in the global equilibrium. Some issues for the retrofitting of dome-like structures are discussed.

Study on Impaired Reinforced Concrete Beams Strengthening with Externally Steel Frame

A large impaired reinforced concrete beam with cracks was strengthened under self-weight action by the externally bonded steel frame composed with bottom steel plate and side hoop steel belts. The normal service loading behaviors of this beam were tested to verify the effectiveness of this strengthening method specified in current Chinese design code. Based on the analyses of test results, it can be concluded that: the deformation of flexural cross section of this beam fitted the assumption of plain cross section, the steel plate could effectively enhance the flexural stiffness and decrease the deflection of this beam, no new cracks appeared under the normal service loads, the cracks at bottom of this beam were more confined by the steel frame than those at web zone. Therefore, other measure should be taken to avoid the opening of web cracks.

Study on Post-Earthquake Corrective Repair of the Stone Archway and Stone Screen in Tiantai Mountain

Abstract: The Qionglai stone archway and stone screen wall are located in Tiantai Mountain, Sichuan Province. Due to the impact of the 5.12 Wenchuan earthquakes, the stone archway began to subside and tilt. The maximum settlement of the two columns in the northeast was 60mm and the vertical deviation was 42mm.The main ridge of the roof which was badly damaged was out of joint and began to fracture, shift and fragment. Other part also got damaged in varying degrees. Due to the special geographical environment, large-scale machinery cannot be put into use. Thus, we can only use small equipment and labor, take advantage of pulley block and set up a steel hoop to improve pillars with jacking and corrective method. At the time of repairment, it should follow the principle of "repair the old as not to change the original appearance" and use the original materials and follow the original process as much as possible so that the stone archway and stone screen wall can be in the original shape.

An effective treatment for penile strangulation

The aim of this study was to present our experience of patients with penile strangulation. The clinical data of 6patients (mean age, 36years; range, 18-72years) with penile strangulation caused by a metal hoop are provided, where the duration of strangulation was between 3h and 1month. Among these patients, the case of a 22-year-old patient with a steel hoop entrapment on his penis for 5days is described; due to serious injury of the skin at the root of penis, an intermediate split‑thickness thigh skin graft was used to repair the skin loss. A review of the literature is also provided in this study, and current treatment options and outcomes are evaluated. In all the cases described, the metal hoops were successfully removed, without gangrene of the penis. These patients were discharged 2-27days later with a satisfactory outcome. Penile strangulation is an unusual clinical condition and the consequences may be severe. The choice of method for removal depends on the type and size of metal hoop, incarceration time, trauma grade and availability of equipment. Early treatment is essential to avoid potential complications, including ischemic necrosis and autoamputation.

Large Span Continuous Girder Bridge Jacking Steel Hoop Stress Analysis

Bridge jacking technology is a new technology in the field of old bridge reconstruction. Based on the case of Beijiang River Bridge jacking of Fokai highway extension engineering, the paper designs steel hoop as jacking force platform. By using ANSYS software, it makes finite element analysis and calculation as well as compares with the experimental data to check the reliability of models. In addition, the paper puts forward the optimization methods of steel hoop based on the analysis of the results. At last, it achieves the objective of saving materials and simplifying installation and use as well as provides guidance for the similar engineering.

Experimental Study of Cyclic Loading Behaviors of Reinforced Concrete Beams Strengthening with Externally Bonded Steel Frame

Two large impaired reinforced concrete beams with pre-loading cracks were strengthened by the externally bonded steel frame composed with bottom steel plate and side hoop steel belts. The cyclic loading behaviors of these beams were tested to verify the effectiveness of this strengthening method specified in current Chinese design code. Based on the analyses of test results, the steel plate worked well with bonded concrete under normal service load, the hoop steel belts were necessary to prevent the peeling of bottom steel plate. The strengthened beams were effectively enhanced in flexural stiffness and ultimate resistance, and no new cracks appeared under the normal service load.

Experimental testing and analytical modeling of CFRP-confined large circular RC columns subjected to cyclic axial compression

A physically informed analytical model which describes the cyclic axial stress–strain behavior of reinforced concrete (RC) columns confined with fiber-reinforced polymer (FRP) composite wraps is necessary for the non-linear analysis and seismic design of such columns. Although extensive studies have been conducted on the monotonic axial behavior of small sized FRP-confined unreinforced concrete columns, there is a lack of research on FRP-confined RC columns and also their cyclic axial response. As a consequence, there is a lack of cyclic axial stress–strain models which can enable seismic response to be reliably simulated by numerical means. Due to such knowledge gaps, this study reports the results of thirty CFRP-confined large-scale unreinforced and RC circular columns subjected to monotonic and cyclic axial compression loading. The test results indicate that the overall shape of the stress–strain curves, the peak compressive stress and strain at failure, the unloading/reloading paths, and also the plastic strain of CFRP-confined concrete are influenced by the CFRP wrap and internal hoop steel reinforcement. On the basis of the experimental results, a cyclic stress–strain model for CFRP-confined circular RC columns is then proposed. The proposed model consists of three main components, namely (i) a monotonically ascending portion to describe the envelope curve, (ii) a polynomial equation to describe unloading paths, and (iii) a straight line to describe reloading paths. The influence of internal hoop reinforcement on the monotonic model, as well as the unloading and reloading responses is also considered. The accuracy of the proposed model is validated with the test data reported in this paper as well as other test results of relevance extracted from the open literature.

Ultimate Bearing Capacity Analysis of Axially Compressive Circular Steel Tube Columns Filled with Bar-Reinforced Concrete

The mechanical behavior and ultimate bearing capacity of the circular bar-reinforced concrete filled steel tube (BRCFST) short columns under axial compression are analyzed in this paper based on the unified strength theory. Considering the restriction effect of steel tube and hoop bar on concrete, the calculation formula of bearing capacity of the column is deduced. Parametric studies are carried out to evaluate the effects of intermediate principal stresses, diameter-thickness ratio of steel tube and the stirrup ratio on the bearing capacity of the column. A good agreement is reached by comparing the results calculated by the formula with the test results. It is concluded that the unified strength theory is applicable in the theoretical analyses of the BRCFST columns.

CFRP-Confined Square RC Columns. II: Cyclic Axial Compression Stress-Strain Model

AbstractFor the seismic design of fiber reinforcement polymer (FRP) confined reinforced concrete (RC) columns, the development of an accurate axial stress-strain model that considers cyclic compression is necessary. In light of such a demand, this paper presents a cyclic axial stress-strain model for FRP-confined RC square columns. The model is informed from physical observations and test measurements obtained from an experimental investigation reported in the companion paper, in which FRP-confined square unreinforced and reinforced concrete columns of larger size under varying cyclic axial compression patterns were tested. In the current paper, the proposed stress-strain model is presented and it consists of three main components, namely (1) a monotonic stress-strain model to describe the envelope curve, (2) a polynomial expression for the unloading path, and (3) a straight line for the reloading path. The influence of internal longitudinal and hoop steel reinforcement is also considered in the proposed ...

CFRP-Confined Square RC Columns. I: Experimental Investigation

The majority of experimental studies investigating the stress-strain behavior of square concrete columns confined with carbon fiber-reinforced polymer (CFRP) composites have focused largely on unreinforced columns of small size. Research on the influence of larger cross section, height, internal steel reinforcement, and initial damage on the axial strength and compressive behavior of CFRP-confined square reinforced concrete (RC) columns is, however, limited. To address such knowledge gaps, this paper presents the results of an experimental investigation on the axial stress-strain behavior of 34 larger-sized square-sectioned RC columns confined with CFRP composite wraps. The primary test variables were (1) cross-sectional dimensions, (2) volumetric ratio of internal hoop steel reinforcement, (3) number of layers of CFRP wrap, (4) nature of loading (i.e., monotonic and cyclic), and (5) damage level before CFRP wrapping. The experiments showed the CFRP wrap to considerably enhance the axial strain capacity but to only slightly increase the axial stress capacity. The experiments also showed the internal reinforcement to influence the shape of the axial stress-strain envelope curve and unloading path and the ultimate axial strain and plastic strain values. Predamage was, however, found to have a small influence. A new confinement pressure model for fiber-reinforced polymer (FRP) confined square RC columns is finally proposed.

Research on Optimizing Precast Water Head on Preloading Filling Spiral Case of a Large-Scale Hydropower Station

In combination with the practice of a pumped storage hydropower station, a 3-D nonlinear finite element method on the preloading filling spiral case is carried out to compare and analyze stresses of the steel spiral case and hoop reinforcement, the stress and bearing ratio of the surrounding concrete, the contact state between the spiral case and concrete in different precast water head. The results indicate that the stress of the surrounding concrete will get better with the increasing of precast water head. But there is a distance between the spiral case and the surrounding concrete when the water head is excessive, which is unhelpful for operating of the unit. When the precast water head of the spiral case is 439m or so, it can play a greater degree of mechanical characteristics of steel and concrete under the premise of operating stably of the unit.

Numerical simulation on seismic retrofitting performance of reinforced concrete columns strengthened with fibre reinforced polymer sheets

This paper evaluates the seismic performance of reinforced concrete columns retrofitted with fibre reinforced polymer (FRP) sheets through numerical simulations of the load–deformation response using two-dimensional finite element analysis (2D-FEA). The relatively rational mesh configuration is verified through comparison of analysis results obtained from the different mesh configurations. The seismic performance of three reinforced concrete (RC) columns strengthened with FRP sheets is assessed through a series of parametric studies, and the applicability of existing crack models and constitutive relationships on crack discontinuity and concrete compressive behaviour are validated. Comparisons of analysis results with tests shows that an equivalent uniaxial strain model and a failure criterion can be used to accurately simulate nonlinear behaviour and the failure of concrete under a biaxial stress state, respectively. Moreover, it is shown that a modified confinement model can be simply adopted to evaluate confined effects from hoop steel and FRP on concrete, which generally operate in three-dimensional confinement. Lastly, the seismic retrofitting performance of RC columns wrapped with FRP sheets is verified by analysing load–deformation responses and the progression of stress–strain at inflection points and bottoms of the columns.

Effect of FRP composites on buckling capacity of anchored steel tanks

Enhancement in the seismic buckling capacity of steel tanks caused by the addition of fiber reinforced polymers (FRP) retrofit layers attached to the outer walls of the steel tank is investigated. Three-dimensional non-linear finite element modeling is utilized to perform such analysis considering non linear material properties and non-linear large deformation large strain analysis. FRP composites which possess high stiffness and high failure strength are used to reduce the steel hoop stress and consequently improve the tank capacity. A number of tanks with varying dimensions and shell thicknesses are examined using FRP composites added in symmetric layers attached to the outer surface of the steel shell. The FRP shows its effectiveness in carrying part of the hoop stresses along with the steel before steel yielding. Following steel yielding, the FRP restrains the outward bulging of the tank and continues to resist higher hoop stresses. The percentage improvement in the ultimate base moment capacity of the tank due to the addition of more FRP layers is shown to be as high as 60% for some tanks. The percentage of increase in the tank moment capacity is shown to be dependent on the ratio of the shell thickness to the tank radius (t/R). Finally a new methodology has been explained to calculate the location of Elephant foot buckling and consequently the best location of FRP application.

Investigation into the Effect of Bonding on FRP-Wrapped Cylindrical Concrete Columns

In this paper the failure of a three layer system comprising a concrete column, an intermediate epoxy layer, and fiber-reinforced polymer (FRP) confinement is investigated. We perform a series of numerical experiments to investigate how the failure loads and ultimate strains of axially loaded plain cement concrete (PCC) and reinforced cement concrete (RCC) columns change with the type of the bond between concrete and epoxy and between epoxy and FRP. Three types of interfacial behavior are considered: rigid, cohesive compliant, and unbonded contact. An idealized spring model for the resultant confinement stiffness is used to explain the effect the nature of the bond has on the results. It is found that the type of bond has a significant effect on the ultimate strength of PCC columns. The results also indicate that the presence of longitudinal and hoop steel reinforcement allows use of comparatively less stiff FRP sheets as confinement material for RCC columns.

Monotonic axial behavior and modelling of RC circular columns confined with CFRP

The retrofit of reinforced concrete columns with FRP jackets has received considerable attention in recent years. The advantages of this technique compared to other similar techniques include the high strength-weight and stiffness-weight ratios of FRP (Fibre Reinforced Plastics), the strength and ductility increase of RC columns confined with FRP jackets as well as the fact that FRP external shells prevent or mitigate environmental degradation of the concrete and consequent corrosion of the steel reinforcement. Furthermore, this method also reduces the column transversal deformation and prevents the buckling of longitudinal reinforcement. Twenty five experimental tests were carried out on reinforced concrete columns confined with CFRP composites, and subjected to axial monotonic compression. In order to evaluate the influence of several parameters on the mechanical behavior of the columns, the height of the columns was maintained, while changing other parameters: the diameter of the columns, the type of material (plain or reinforced concrete), the steel hoop spacing of the RC columns and the number of CFRP layers. Predictive equations, based on the experimental analysis, are proposed to estimate the compressive strength of the confined concrete, the maximum axial load and the axial or the lateral failure strain of circular RC columns jacketed with CFRP. A stress–strain model for CFRP confined concrete in compression, which considers the effect of the CFRP and the transversal reinforcement on the confined compressive strength of the column is also proposed. The curves, axial load versus axial or lateral strain of the RC column, are simulated based on the stress–strain model and include the longitudinal reinforcement effect. The results demonstrate that the model and the predictive equations represent very well the axial compression behavior of RC circular columns confined with CFRP. The applicability of this model to a large spectrum of RC column dimensions is its main advantage.

Emergency management of penile strangulation: a case report and review of the Chinese literature

A 36-year-old Chinese man presented to the emergency department with a steel hoop entrapment on his penis for 10 h. The constricting steel hoop was 20 mm in external diameter,...

Seismic Rehabilitation of Reinforced Concrete Frame Interior Beam-Column Joints with FRP Composites

An experimental research program is described regarding the use of externally applied carbon fiber-reinforced plastic (CFRP) jackets for seismic rehabilitation of reinforced concrete interior beam-column joints, which were designed for gravity loads. The joints had steel reinforcement details that are known to be inadequate by current seismic codes in terms of joint shear capacity due to the absence of transverse steel hoops and bond capacity of beam bottom steel reinforcing bars at the joint. Lap splicing of beam bottom steel reinforcement at the joint using externally applied longitudinal CFRP composite laminates is investigated. Improvement of joint shear capacity using diagonal CFRP composite laminates is another strengthening scheme employed. Concrete crack widths for the as-built specimens and the extent of CFRP delamination for the rehabilitated specimens at various drift ratios are reported. The test results indicate that CFRP jackets are an effective rehabilitation measure for improving the seismic performance of existing beam-column joints with inadequate seismic details in terms of increased joint shear strength and inelastic rotation capacity. In addition, CFRP laminates are effective rehabilitation measures for overcoming problems associated with beam bottom steel bars that have inadequate embedment into the beam-column joints.