Maria J. Favvata

ASSESSMENT OF MULTISTORY RC BUILDINGS SUFFERING INTER-STORY POUNDING

Abstract. The pounding of adjacent RC frames with different heights is studied. The main issue behind this investigation is the influence of the local behaviour of the columns that suffer the hit from the slabs of the adjacent building during the seismic excitation. This column’s requirements for ductility and shear capacity have been proven to be the critical parameters for the behaviour and final performance of the whole structure. These parameters can be designed in order the obtained performances to satisfy the seismic demands of the Eurocodes. In this study the critical column’s requirements for ductility and shear capacity are evaluated for three seismic demands based on Eurocode 8-part3: (a) demand for Damage Limitation limit state that corresponds to ground motions with return periods of 225 years (b) demand for Significant Damage limit state that corresponds to ground motions with return periods of 475 years and (c) demand for Near Collapse limit state that corresponds to ground motions with return periods of 2475 years. The evaluated requirements are for seven different seismic excitations that have been properly scaled to fit the Eurocode’s three seismic demands of low zone of seismic hazard. Afterwards, the minimum required gap distances between the adjacent structures are evaluated taking into account the local capacities of the columns that suffer the inter-story pounding effect. These results are compared with the corresponding limitations for adequate gap distances that are provided by the Eurocode 8. The results show that even in the case of Damage limitation seismic demand special measures have to be taken for the column of the multistory RC frame that suffers the hit. The seismic performance of the columns at a specific limit state of the assessment should be considered for the estimation of an adequate gap distance between the adjacent structures. Thus, the minimum gap distance that is required in order to eliminate the possibility for interaction between adjacent structures depends on the limit state of the assessment. Eurocode’s provisions for adequate gap separation do not depend on the seismic demand (limit state) but in any case based on the results of this study these provisions seem to be conservative.

The Inter-storey Pounding Effect on the Seismic Behaviour of Infilled and Pilotis RC Structures

The influence of the inter-storey structural pounding on the seismic behaviour of adjacent multistorey reinforced concrete structures with unequal storey heights is studied taking into account the local response of the infill panels. Results of more than 100 dynamic analyses indicate that the most important issue in the interaction between structures is the local response of the column of the tall structure that suffers the hit of the upper floor slab of the adjacent shorter and stiffer structure. This column appears to be in most of the times in a critical condition due to shear action. In this paper, the influence of the infill panels on the pounding problem of adjacent structures is studied. Two types of masonry-infilled structures are considered: (a) infilled frame and (b) infilled frame without infills at the base storey (pilotis frame). Results in terms of inter-storey drifts, shear requirements, ductility requirements and infill local seismic response are presented. The influence of the infill panels on the seismic performance of the critical column that suffers the hit led in all examined cases to an increase of the demands for shear and ductility, when compared to the corresponding values that are developed in the cases that the RC structure is studied without considering the infills. Thus, it can be demonstrated that in all examined inter-storey pounding cases, the presence of the infills was not enough for the amelioration of the excessive demands for shear and ductility of the column that suffers the impact. Nevertheless, the presence of the masonry infill panels has been proved as an important parameter for the safety of the building. Non-linear dynamic step-by-step analyses and special purpose elements are employed for the needs of this study.

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.