Constantin E. Chalioris

EFFECTIVENESS OF RC BEAM-COLUMN CONNECTION REPAIR USING EPOXY RESIN INJECTIONS

The effectiveness of a technique for the repair of reinforced concrete beam column connections, damaged due to cyclic loading, is experimentally investigated. The applied technique is mainly based on the use of thin epoxy resin infused under pressure into the crack system of the damaged joint body. Special attention is given to the examination of the repair efficiency with reference to the shear reinforcement of the joint. To achieve this purpose, the test program included 17 exterior connection specimens covering all commonly used joint reinforcing practices. Specimens were initially subjected to increasing full cyclic imposed deformation until the cycle maximum load decreased to 40% of the yield load level measured in the first cycle. After repair, all specimens were retested in the same way. Conclusions concerning the effectiveness of the applied repair technique, based on maximum cycle loads, loading stiffness, and hysteretic energy absorption capabilities of the tested specimens, are drawn and commented upon. Remarks concerning the influence of different design reinforcement arrangements on the behaviour of the joints are also included. The examined repair technique can be considered to be satisfactory, since all repaired joints exhibited equal or higher response load values and loading stiffness compared to the virgin ones, and tended to undergo more full loading cycles without a significant loss of strength.

Damage Evaluation in Shear-Critical ReinforcedConcrete Beam using Piezoelectric Transducers asSmart Aggregates

Abstract Damage detection at early cracking stages in shear-critical reinforced concrete beams, before further deterioration and their inevitable brittle shear failure is crucial for structural safety and integrity. The effectiveness of a structural health monitoring technique using the admittance measurements of piezoelectric transducers mounted on a reinforced concrete beam without shear reinforcement is experimentally investigated. Embedded “smart aggregate” transducers and externally bonded piezoelectric patches have been placed in arrays at both shear spans of the beam. Beam were tested till total shear failure and monitored at three different states; healthy, flexural cracking and diagonal cracking. Test results showed that transducers close to the critical diagonal crack provided sound and graduated discrepancies between the admittance responses at the healthy state and thedamage levels.Damage assessment using statistical indices calculated from the measurements of all transducers was also attempted. Rational changes of the index values were obtained with respect to the increase of the damage. Admittance responses and index values of the transducers located on the shear span where the critical diagonal crack formed provided cogent evidence of damage. On the contrary, negligible indication of damage was yielded by the responses of the transducers located on the other shear span, where no diagonal cracking occurred.

Rehabilitation of Shear-Damaged Reinforced Concrete Beams Using Self-Compacting Concrete Jacketing

The application of a reinforced self-compacting concrete jacket for the structural rehabilitation of shear damaged reinforced concrete beams is experimentally investigated. Five beams were constructed and subjected to monotonic loading in order to exhibit shear failure. The damaged specimens were restored using relatively thin reinforced jackets and retested by the same four-point bending loading. The self-compacting concrete jacket applied, encasing the bottom width and both vertical sides of the initially tested beams (U-formed jacketing), has a small thickness (25 mm) and includes small (5) steel bars and U-formed stirrups. Test results and comparisons between the experimental behaviour of the beams indicated that the examined jacketing technique is a reliable rehabilitation method since the capacity of the retrofitted beams was fully restored or ameliorated with respect to the initial specimens. Discussion of the ability of the applied jacket to enhance the overall structural performance of the examined beams and, potentially, to alter their failure mode to a more ductile one is also included. Calculations of the flexural and shear strength of the tested beams and evaluation of the monolithic factors for the capacity at yield and at ultimate of the jacketed beams were also performed and are commented on.

Application of a Reinforced Self-Compacting Concrete Jacket in Damaged Reinforced Concrete Beams under Monotonic and Repeated Loading

This paper presents the findings of an experimental study on the application of a reinforced self-compacting concrete jacketing technique in damaged reinforced concrete beams. Test results of 12 specimens subjected to monotonic loading up to failure or under repeated loading steps prior to total failure are included. First, 6 beams were designed to be shear dominated, constructed by commonly used concrete, were initially tested, damaged, and failed in a brittle manner. Afterwards, the shear-damaged beams were retrofitted using a self-compacting concrete U-formed jacket that consisted of small diameter steel bars and U-formed stirrups in order to increase their shear resistance and potentially to alter their initially observed shear response to a more ductile one. The jacketed beams were retested under the same loading. Test results indicated that the application of reinforced self-compacting concrete jacketing in damaged reinforced concrete beams is a promising rehabilitation technique. All the jacketed beams showed enhanced overall structural response and 35% to 50% increased load bearing capacities. The ultimate shear load of the jacketed beams varied from 39.7 to 42.0 kN, whereas the capacity of the original beams was approximately 30% lower. Further, all the retrofitted specimens exhibited typical flexural response with high values of deflection ductility.

CAPACITY OF RC JOINTS SUBJECTED TO EARLY-AGE CYCLIC LOADING

The influence of cyclic loading applied on T-shape beam-column subassemblies at an early stage of the concrete curing period on the capacity of the joints after the maturing period is experimentally investigated. A series of 20 joints constructed for this purpose were subjected first to an early-age cyclic loading and then retested at the age of 28 days. From the results it is deduced that the early-age loading has significantly influenced the capacity and the overall behaviour of the specimens after the concrete curing period. Specimens subjected to early-age loading 12 or 24 hours after casting exhibited at the age of 28 days peak load values and energy dissipation higher than the ones of the specimens subjected to early-age loading two or seven days after casting, due to the high recoverability of the material at the very early stages of concrete curing period. Emphasis has been placed on the study of the influence of the early-age loading sequence and the slippage of the bars anchorage on the final capacity of the examined specimens. Finally, an attempt is made to assess the damage caused by early-age loading based on the observed stiffness degradation.

Recording and Rehabilitation Procedures for Historic Masonry Buildings

The use of photogrammetric surveys for the recording of the structural system status for historic masonry buildings is a new and sound tool for in-depth pathology understanding and rehabilitation decision-making. In this study, the structural system of two historic masonry buildings is investigated based on the recording data obtained via photogrammetry. The first one is a four-storey traditional tobacco warehouse of the late 19th century in Alexandroupolis, Northern Greece, which has been partially collapsed in 2005 and constituted an extremely dangerous working environment. Therefore, the photogrammetric recording was the only really accurate and safe in situ measurement procedure of the existing damaged structural system of the building. The second one is an old customs house located in the old historic town of Nafplio, Southern Greece, and specifically in front of the central part of the port. It was built around the middle of the 19th century by the well-known Architect S. Kleanthis. Its architectural, structural and morphological characteristics along with its artistic details have been excellently brought out through the advanced method of photogrammetry. Simultaneously, this detailed display of the structural system pointed out its pathology. This way, all the necessary information for the presented structures have been acquired with an appropriate accuracy in order to assist the Engineer to choose the proper repairing and strengthening techniques for the renovation and the re-use of these historic buildings; finally proposed rehabilitation techniques are also presented. The recording procedure used, combines the conventional topographic surveys and the photogrammetric image processing for the formation of all the facades’ orthoimages. The orthoimages were used as background information to digitize details of the buildings facades in a CAD environment. The Photomodeler software and the freeware application Hugin has been used to create respectively a detailed 3D model and an interactive panorama file of the buildings. A proper intervention plan is presented and commented for each building.

REHABILITATION OF A PARTIALLY COLLAPSED MASONRY TRADITIONAL TOBACCO WAREHOUSE OF THE LATE 19TH CENTURY

This study presents morphology, pathology, recording method, applied rehabilitation procedure and constructional problems of a four-storey masonry building in Alexandroupoli which today is partially collapsed. It was constructed before 1900 and enlarged in 1924 to be used as tobacco warehouse. From 1950s onwards, it has been neglected and because of the total lack of maintenance it has sustained structural and architectural deterioration; intervention works for its re-use as Municipal Library began in 2004. The first approved rehabilitation plan based on false strategy adopted the total removal of the interior structural members including wooden diaphragms, beams and columns and the construction of a new internal reinforced concrete frame structure. It proved to be catastrophic since in 2005 a sudden partial collapse of masonry and the roof was caused. The building has remained partially collapsed and difficult to approach due to the danger of a potential further collapsing. Recording of the present state has been based on photogrammetry. A proper intervention plan is applied. This work is a contribution in the field of structural rehabilitation of partially collapsed historic masonry buildings that constitute an extremely unsafe working environment.

STRUCTURAL UPGRADING OF A 3-STOREY HERITAGE STRUCTURE OF 1925 IN THESSALONIKI

Abstract. The structural upgrading and rehabilitation procedure of a historic building representative of 1920s construction in Thessaloniki, Greece is presented. The case study building is a listed three-storey reinforced concrete flat-slab frame structure sited in Nikis Avenue in front of the old seaside of the city of Thessaloniki. Reinforced concrete columns and beams frames along with wide infilled masonry walls are the load-bearing elements of the structure. The building was designed in 1925 without Seismic Code requirements and constructed in 1926. The ground floor was used for many years as a cinema, whereas the upper floors are areas where people may congregate since they are used as assembly halls (dining halls, reading and conference rooms). Concrete core tests and in-situ non-destructive tests were first performed to evaluate the compressive strength of the concrete and to detect determine the existing steel reinforcements of the reinforced concrete members. The concrete strength was low and the steel reinforcement of several columns of the ground floor and slabs of the upper floors was found to be corroded. Analytical evaluations of the original and the strengthened structure were carried out in order to identify the weak members of the structural system and to justify the decisions of the strengthening methods adopted. Comparisons between the capacity of the existing or/and the strengthened members with the design requirements derived from the initial and the strengthened structural system analyses are also presented. Special attention has been given in issues regarding the simulation of actual details encountered in mixed structural system. The upgrading methods used along with the uncovering of latent defects during the strengthening works and how these were managed are also commented in this paper.

Optimum Dosage of Deformed Steel Fibres in Fibrous Concrete Beams under Predominant Shear

This study presents an analytical approach to evaluate an optimum content of deformed steel fibres in shear-dominated fibrous concrete beams in order strength and ductility requirements to be satisfied. The proposed methodology is based on the calculations of the flexural and shear capacities and to the concept that a pure flexural response should be achieved. The goal of this method is to evaluate the minimum required value of the fibre factor, F, which expresses the effect of the volume fraction and the geometrical characteristics of the used steel fibres. The calculation of F is achieved using a cubic formula derived from the described procedure. Fibres can be used either as the only shear reinforcement or in combination with stirrups. Test results from 47 beams of the literature are used to verify and to illustrate the application of the proposed approach. Comparisons between experimental and predicted results showed a very good agreement. Design charts have also been plotted by the implementation of this methodology as an analysis tool.