Short Lap Splices Research Articles

Seismic performance of lap-spliced pre-damaged and intact concrete columns strengthened or retrofitted with UHPC and NSM

Reinforced concrete (RC) columns with deficient lap splice details such as short lap splice length and widely spaced stirrups were vulnerable to earthquakes. In the present study, to evaluate the effectiveness of an innovative retrofitting technique using the combination of ultra-high performance concrete (UHPC) and near surface mounted (NSM) technique on the seismic performance of RC columns with deficient lap splices details, cyclic loading tests were performed on four large-sized RC column specimens. Two RC columns were strengthened with UHPC or the combination of UHPC and NSM, and the other two were retrofitted with the combination of UHPC and NSM after the lateral strength decreased to 85% peak strength during the pre-damage cyclic tests. The load–displacement relationship, stiffness degradation, energy dissipation, and residual displacement of RC columns are evaluated. The test results showed that the peak strength and ductility of RC columns with deficient lap splice are significantly improved after strengthening or retrofitting with the combination of UHPC and NSM. The seismic performance of severely damaged RC columns due to deficient lap splice details can still be effectively restored after retrofitting with the combination of UHPC and NSM. Considering the adverse effect of pre-damage, a design method is proposed to predict the flexural capacity of RC columns retrofitting with UHPC or the combination of UHPC and NSM. The proposed method is also applied to predict the flexural capacity of RC beams strengthened with UHPC. The proposed method predicted well the test results of this study and existing tests.

Performance of Steel Bar Lap Splices at the Base of Seismic Resistant Reinforced Concrete Columns Retrofitted with FRPs—3D Finite Element Analysis

This paper examines analytically the design criteria for the composite retrofit of reinforced concrete (RC) columns with a short lap splice length of steel rebars inside the critical region. The advanced potential of pseudo-dynamic three-dimensional (3D) finite element (FE) modelling is utilized to investigate critical design parameters for the required carbon fiber-reinforced polymer (FRP) jacketing of RC columns with a rectangular cross-section based on the experimental lateral force-to-drift envelope behavior of characteristic cases from the international literature. The satisfactory analytical reproduction of the experimental results allows for the systematic numerical investigation of the developed stress along the lap splice length. The maximum lateral force and the horizontal displacement ductility of the column, as well as the maximum developed tensile axial force on the longitudinal bars, their variation along the lap, the bar yielding, and the plastic hinge length variation, are considered to determine the seismic behavior of the columns. For the first time, cases of smooth bar slip together with delayed bar yielding or without bar yielding are identified that may be recorded through a “ductile” P-d seismic response. Such pseudo-ductile response cases are revisited through suitably revised redesign criteria for adequate FRP jacketing.

Seismic assessment of reinforced concrete columns with short lap splices

Existing reinforced concrete (RC) columns with short splices in older-type frame structures are prone to either a shear or bond mechanism. Experimental results have shown that the force–displacement response of columns exhibiting these failure modes are different from flexure-critical columns and typically have lower deformation capacity. This article presents a failure mode-based approach for seismic assessment of RC columns with short splices. In this approach, first, the probable failure mode of the component is evaluated. Subsequently, based on the failure mode, the force–displacement response of the component can be predicted. In this article, recommendations are proposed for evaluating the probable failure mode, elastic rotation, drift at lateral failure, and drift at axial failure for columns with short splices experiencing shear, flexure, or bond failures.

Methodology for Regularization of Force-Based Elements to Model Reinforced Concrete Columns with Short Lap Splices

In reinforced concrete structures built before the 1970s, it was common for columns to be constructed with short lap splices and widely spaced transverse bars at the column base, leading to increased likelihoods of pull-out failures and structural collapse during seismic events. In the modeling and analysis of reinforced concrete columns with short lap splices, several challenges arise, particularly with softening behavior that leads to strain localization and scaling and convergence issues in analyses. This research presents a methodology to regularize force-based beam-column elements with softening lap-splice material response. In the methodology, a constant energy release criterion is imposed with the constant postpeak energy of the lap-splice region determined from relevant experimental data. With the proposed regularization, the numerical model shows objective results that are independent of the length of the element and number of integration points used. Whereas the accuracy in estimating, for example, the displacement at 20% strength drop using existing nonregularized models changes with the number of integration points, the accuracy using the proposed model remains constant across numbers of integration points used with a mean accuracy of 94% compared with experimental tests. Results from static pushover and cyclic analyses show an order of magnitude decrease in standard deviation of the response using the regularized model. Increased accuracy and increased convergence for the method across the number of integration points used is shown in static and dynamic analyses. The proposed regularization approach is able to alleviate strain localization issues and facilitates the scaling of analyses from small-scale to full-scale structures.

Cyclic behaviour of lightly-reinforced concrete columns with short lap splices subjected to unidirectional and bidirectional loadings

Reinforced concrete (RC) buildings constructed prior to the 1970s could be vulnerable to earthquakes due to inadequate reinforcement details such as widely spaced transverse reinforcement and short lap splices. Most of these buildings were designed without considering seismic loads. The objective of this study was to investigate the cyclic behaviour of the lightly reinforced concrete columns with short lap splices in older RC buildings under unidirectional and bidirectional loadings. Experimental tests were conducted using four full-scale specimens. The estimates of modelling parameters and lateral strength obtained from the measured cyclic curves of the specimens were compared with the values calculated according to ASCE 41-17. Cyclic behaviour of lightly-reinforced columns with short lap splices was significantly affected by loading types and the levels of axial load. The modelling parameters and lateral strength were also affected by the levels of axial load and by loading types (unidirectional and bidirectional) deviating from the constant values specified in ASCE 41-17 for these parameters.

Impact of corrosion on risk assessment of shear-critical and short lap-spliced bridges

Increasing corrosion in aging reinforced concrete structures is increasing their vulnerability to failures. This is particularly true for bridges with low-ductility columns, including shear-critical columns and columns with short lap splices. This paper presents a methodology to assess the impact of corrosion on performance of these structures. The combined analytical and numerical modeling of shear-critical and lap-spliced columns is detailed, and outcomes are verified with previous experimental test data. Corrosion effects are accounted for through reduction of longitudinal and transverse reinforcement and bond deterioration between the steel and concrete through corrosion-induced cracking. The impact of corrosion on risk is assessed through conducting fragility analyses. Results quantify the increase in failure probabilities of these structures, measured by increasing probabilities of exceeding defined damage states, with increasing levels of corrosion. Corrosion is found to have a larger impact on increasing probabilities of exceeding more severe damage states. Twenty percent mass loss of reinforcement increases the probability of exceeding the complete damage state by up to 49% and 34% for a shear-critical and lap-spliced column, respectively. The effect is more pronounced at intermediate loading intensities, where there is uncertainty about the performance of the structure. Comparing between failure modes, bridges with columns of short lap splice are more vulnerable to collapse under the same degree of corrosion compared with shear-critical columns.

Experimental study of strand splice connections in UHPC for continuous precast prestressed concrete bridges

Current infrastructure demands require bridging larger spans while maintaining construction and structural simplicity. The use of standard prestressed concrete girder elements which might be spliced in situ has been regarded as an appealing solution. This study investigated the performance of strand lap splices embedded in ultra high performance concrete (UHPC) and their further implementation in structural continuity connections for spliced girder bridges. The results of an initial experimental program suggested that the full development length of 12.7mm and 15.2mm diameter unstressed prestressing strands embedded in a steel fiber reinforced UHPC is approximately 510 and 610mm (40 ds), respectively. The implementation of the splice strand connection concept for girder spliced bridges was further developed and experimentally assessed. Two full scale box beam tandems were spliced and tested. It was demonstrated that large flexural capacity can be achieved with relatively short lap splice lengths. Approximately 90% of the ultimate flexural capacity estimated for the fully prestressed and continuous girder was reached by the spliced box beam tandem connected using a strand splice length of 762mm (50 ds). Additional detailing of the structural system and the reinforcing scheme is discussed to improve the performance of the system in general and the connection in particular.

Strengthening of short splices in RC beams using Post-Tensioned Metal Straps

This paper investigates the effectiveness of a novel and cost-effective strengthening technique using Post-Tensioned Metal Straps (PTMS) at enhancing the bond behaviour of short lap spliced steel bars in reinforced concrete (RC) beams. Twelve RC beams with a short lap splice length of 10d b (d b = bar diameter) at the midspan zone were tested in flexure to examine the bond splitting failure. The effect of confinement (no confinement, internal steel stirrups or external PTMS), bar diameter and concrete cover were examined. The results show that, whilst unconfined control beams failed prematurely due to cover splitting, the use of PTMS confinement enhanced the bond strength of the spliced bars by up to 58 % and resulted in a less brittle behaviour. Based on the test results, a new analytical model is proposed to predict the additional bond strength provided by PTMS confinement. The model should prove useful in the strengthening design of substandard lap spliced RC elements.

Effectiveness of R/C jacketing of substandard R/C columns with short lap splices

The effectiveness of a retrofitting method for concrete columns with particular weaknesses is experimentally evaluated and presented in this paper. Structural deficiencies namely the inadequacy of transverse reinforcement and short length of lap splices are very common in columns found in structures built prior to the 1960s and 1970s. Recent earthquakes worldwide have caused severe damages and collapses of these structures. Nevertheless, the importance of improving the load transfer capacity between the deficiently lap-spliced bars is usually underestimated during the strengthening procedures applied in old buildings, though critical for the safety of the residents\' lives. Thus, the seismic performance of the enhanced columns is frequently overestimated. The retrofitting approach presented herein involves reinforced concrete jacketing of the column sub-assemblages and welding of the lap-spliced bars to prevent the splice failure and conform to the provisions of modern design Codes. The cyclic lateral loading response of poorly confined original column specimens with insufficient lap splices and the seismic behavior of the retrofitted columns are compared. Test results clearly demonstrate that the retrofitting procedure followed is an effective way of significantly improving the seismic performance of substandard columns found in old buildings.

Damages of minarets during Erciş and Edremit Earthquakes, 2011 in Turkey

This paper illustrates the damages of reinforced concrete and masonry minarets during October 23 (Erciş) and November 9 (Edremit), 2011 Van earthquakes in Turkey. Erciş and Edremit are townships located 90km and 18km from Van city center in Turkey, respectively. Ground accelerations and response spectrums for these earthquakes are given in this paper. A total of 63 reinforced concrete and masonry minarets are heavily damaged or collapsed in the city center and villages nearby after both earthquakes. Because of the fact that there is no Turkish standard and specification directly related to design of minarets, nearly all of the constructions are carried out by workers using only their own technical knowledge. So, all of the non-engineering reinforced concrete and masonry minarets completely collapsed or damaged heavily. From the study, it is seen that the damages are due to several reasons such as site effect, location, and length of the fault, reduction in cross section and formation of the discontinuity, use of plain reinforcement steel, use of concrete with insufficient strength, existence of short lap splices and incorrect end hook angle, larger mass and stiffness concentrations on some region, longitudinal reinforcements discontinuity, cracks at the cylindrical body, and damage of spire and end ornament. In addition to these reasons, the two earthquakes hit the minarets within seventeen days, causing progressive damage. So, the existing design and construction practices should be improved to provide sufficient earthquake performance. Also, it is recommended that there should be a safe distance between the minaret and surrounding structures to reduce the loose of life after earthquake.

Bond strength of short lap splices in RC beams confined with steel stirrups or external CFRP

This paper investigates the bond behaviour of lapped steel bars using fifteen RC beams tested in flexure. Twelve of the beams were designed to fail by bond splitting at midspan, where the main flexural reinforcement was lapped 10 bar diameters. The parameters studied include the amount and type of confinement at midspan (no confinement, internal steel stirrups or externally bonded carbon FRP), concrete cover and bar size. The results show that the CFRP confinement enhanced the bond strength of the lapped bars by up to 49 % with reference to unconfined beams, and improved significantly the overall behaviour of the specimens. The experimental results are compared with existing models to predict the bond strength enhancement provided by CFRP confinement. It is shown that existing models overestimate considerably the CFRP strains and show a large scatter when predicting experimental results. Based on the test results, a new approach to predict the bond strength enhancement due to CFRP confinement is proposed. This can be used during the assessment and strengthening of substandard RC constructions.

Damages on reinforced concrete buildings due to consecutive earthquakes in Van

Consecutive earthquakes occurred on October 23rd, 2011 in Ercis and on November 9th, 2011 in Edremit that are townships located 90km and 18km far from Van city in Turkey, respectively. A total of 28,000 buildings were damaged or collapsed in the city center and the surrounding villages after the Ercis earthquake. This number reached 35,000 after the Edremit earthquake. In the area where the earthquakes occurred, almost all the reinforced concrete buildings were affected.This study presents field observations of damages on reinforced concrete buildings due to the consecutive earthquakes that occurred in Van, Turkey. Damages appearing in the buildings may occur due to several reasons such as site effect, poor construction quality, poor concrete strength, poor detailing in beam-column joints, detailing of stronger beam than column, soft stories, weak stories, inadequate reinforcement, short lap splices, incorrect end hook angle, and short columns. Aftershocks also caused progressive damages on the buildings within 17 days after the earthquakes. According to the results of this study, most of the damaged buildings were not designed and constructed according to the Turkish earthquake code, the so-called Specification for Buildings to be built in Seismic Zones.

Performance and damages of reinforced concrete buildings during the October 23 and November 9, 2011 Van, Turkey, earthquakes

In this paper, it aimed to investigate the performance and damages of reinforced concrete buildings during October 23 (Erciş) and November 9 (Edremit), 2011 Van earthquakes in Turkey. A total of 28,000 buildings are damaged or collapsed in the city center and surrounding villages after the Erciş earthquake. This number increased to 35,000 after the Edremit earthquake. Large proportion of non-engineering reinforced concrete buildings completely collapsed or were damaged heavily. Most of the reinforced concrete buildings in the affected area are not designed and constructed in accordance with Turkish Earthquake Resistant Design Code. The cracking and failure patterns of the reinforced concrete buildings are examined. Seismic code requirements are discussed and compared with observed details. It is seen that the damages are due to several reasons such as site effect, location, and length of the fault, the poor construction quality, the poor concrete strength quality and unribbed reinforcement steel, poor detailing in beam column joints, strong beam–weak columns, soft stories, weak stories, inadequate transverse reinforcement, existence of short lap splices and incorrect end hook angle, short columns, weak walls, inadequate safe distance between buildings, unconfined gable walls, concrete slab failures, insulation materials, broken staircase slab and cracks at the corners of the windows and doors. Also, it is emerged that 26% of the buildings have no building license, 66% of the buildings' ground floor is used as a shop, 36% of the buildings have no static project, building (static) projects of 57% of the structures are insufficient, 57% of the buildings are not constructed in accordance with their static project, 74% of the static projects have no detail drawings and hoops densifications, the majority of the buildings have not got sufficient compressive strength according to the related earthquake code, aggregate dimensions are larger than maximum aggregate diameter for concrete, 60% of the building was constructed using un-ribbed reinforcement steel, and the majority of the buildings (85%) have not got any soil report. In addition to these reasons, the two earthquakes hit the reinforced concrete buildings within 17 days, causing progressive damage.

Effect of Lap Splices on Flexural Resistance and Cyclic Deformation Capacity of RC Members

Short lap splices in vertical members are a typical and critical deficiency in existing structures in seismic zones, especially when the splice is located at the bottom end of the member, i. e., in the plastic hinge region. Wrapping the lap-splice region of the member with fibre-reinforced-polymers (FRP) is becoming the method of choice for remedying this deficiency. Test results from the international literature are used in the paper to develop simple rules for the calculation of the flexural resistance and of the yielding or ultimate deformations of concrete members of various cross-sectional shapes, as these affected by short lap-splicing in the plastic hinge region and by FRP wrapping of the length of the member with deficient lapping.

Inelastic Analysis of Reinforced Concrete Columns with Short Lap Splices Subjected to Reversed Cyclic Loads

A common deficiency in reinforced concrete columns built in the early 1970s or before is the detailing of lap splices. These splices are often short, poorly confined, and located immediately above the floor level where large inelastic demands can be expected during seismic actions. In this paper, an analytical model for estimating the seismic response of reinforced concrete columns with short lap splices is presented. The model is based on a local bond stress-slip relationship to estimate the bar stress and deformation at splice failure and includes degradation of stiffness and strength with increasing deformation amplitude and with the number of reversed cyclic lateral deformations. The proposed analysis procedure is validated against experimental data from cyclic loading tests on reinforced concrete columns with typical construction details of the early 1970s. The results show that. the strength of short lap splices can be predicted well using local bond-slip models derived from isolated anchored bars. Also, the calculated failure mode, lateral load resistance, and deformation corresponding to the splice failure were in good agreement with the measured values. A simple equation for calculating the bar stress at splice failure is presented as well. Use of the proposed equation resulted in excellent agreement between the measured and calculated strength at splice failure.