Chrysanthos Maraveas

Post-fire assessment and reinstatement of steel structures

Purpose This paper aims to present technical aspects of the assessment method and evaluation of fire damaged steel structures. The current work focuses on the behavior of structural normal steel (hot-rolled and cold-formed) and high-strength bolts after exposure to elevated temperatures. Information on stainless steel, cast iron and wrought iron is also presented. Design/methodology/approach Because of the complexity of the issue, an elaborate presentation of the mechanical properties influencing factors is followed. Subsequently, a wide range of experimental studies is extensively reviewed in the literature while simplified equations for determining the post-fire mechanical properties are proposed, following appropriate categorization. Moreover, the reinstatement survey is also comprehensively described. Findings Useful conclusions are drawn for the safe reuse of the structural elements and connection components. According to the parametric investigation of the aforementioned data, it can be safely concluded that the most common scenario of buildings after fire events, i.e. apart from excessively distorted structures, implies considerable remaining capacity of the structure, highlighting that subsequent demolition should not be the case, especially regarding critical infrastructure and buildings. Originality/value The stability of the structure as a whole is addressed, with aim to establish specific guidelines and code provisions for the correct appraisal and rehabilitation of fire damaged structures.

Pushover Analysis of Steel Seismic Resistant Frames with Reduced Web Section and Reduced Beam Section Connections

The widespread brittle failure of welded beam-to-column connections caused by the 1994 Northridge and 1995 Kobe earthquakes highlighted the need for retrofitting measures effective in providing ductility to connections. Researchers presented the reduced beam section (RBS) as a viable option to prevent brittle failure at the connection weld. More recently, an alternative connection known as a reduced web section (RWS) has been developed as a potential replacement, and initial studies show ideal performance in terms of rotational capacity and ductility. This study performs a series of non-linear static pushover analyses using a modal load case on three steel moment-resisting frames (MRFs) of 4-storeys, 8-storeys and 16-storeys. The frames are studied with three different types of connections; fully-fixed moment connections, RBS connections and RWS connections, in order to compare the differences in capacity curves, inter-storey drifts and plastic hinge formation. The seismic-resistant connections have been modelled as non-linear hinges in ETABS, and their behaviour have been defined by moment-rotation curves presented in previous recent research studies. The frames are displacement controlled to the maximum displacement anticipated in a 2 in 50 earthquake. The study concludes that RWS connections perform satisfactorily when compared with frames with fully-fixed moment connections in terms of providing consistent inter-storey drifts in low to mid-rise frames, without significantly compromising the overall strength capacity of the frames. The use of RWSs in taller frames causes an increase in inter-storey drifts in the lower storeys, as well as causing a large reduction in strength capacity. Frames with RWS connections behave comparably to frames with RBS connections and are deemed a suitable replacement.

Optimal Design Of Through-truss Steel Bridges

Structural optimisation is a topic which gathers the interest of many research teams and engineers. Its purpose is to minimise an objective function, such as the weight of a structure, subjected to certain constraints (e.g. compliance of structural members with code requirements). In this paper, optimal design (in terms of shape and sizing) of through-truss steel bridges is performed. Several cases of simply supported bridges with different spans (40m, 50m and 60m) and varying width, corresponding to one or two traffic lanes, were examined. For the aforementioned bridges, the effect of three deck types (reinforced concrete deck, fiber reinforced polymer deck and steel deck) on the weight of the truss and the total weight was investigated. Least-weight shape and sizing optimal design was executed, with the height of the truss and the cross-section areas of its members constituting the design variables of the problem. The structural analysis and design were conducted in accordance with the specifications of the Eurocodes. The influence of both the height-to-span ratio and the deck type on the weight of the truss, the total weight and the cost is discussed based on the results obtained from the optimisation procedure.

Fire resistance of DELTABEAM® composite beams: a numerical investigation

Purpose The DELTA® beam composite floor system is a recently developed shallow floor type that has seen many applications in contemporary construction. It involves partially encasing DELTA® steel beams in concrete, with the lower flange remaining exposed. Besides the satisfactory behavior of the system at ambient conditions, understanding its response under elevated temperatures is critical in evaluating its overall performance. Despite certification from the manufacturing company that the system has adequate fire resistance, its behavior under fire conditions has neither been investigated to depth nor reported in detail. The purpose of this paper is the detailed numerical investigation of their behavior in fire. For this reason, the finite element method was implemented in this paper to simulate the response of such beams subjected to fire. Material properties were modeled according to the Eurocodes. The coupled thermal-structural parametric analyses involved four different variations of the “shortest” and “deepest” cross-section (eight case studies in total) specified by the manufacturing company. Other simulations of these cross-sections, in which either the thermal expansion or the structural load were not taken into account, were carried out for comparison purposes. Design/methodology/approach The methodology for simulating such systems, which has been successfully implemented and validated against fire test results elsewhere (Maraveas et al., 2012) was also followed here. To investigate the statement made by Maraveas et al. (2014) and the equations proposed by Zaharia and Franssen (2012) that the insulation is not so effective for “short” cross-sections, two beams, one with a D20-200 (Deltabeam Technical Manual, 2013) cross-section (shallowest section) and one with a D50-600 (Deltabeam Technical Manual, 2013) cross-section (deepest section), were simulated in this paper for comparison purposes. Additionally, reasonable assumptions were made for the cross-sectional dimensions not specified by the manufacturer (Deltabeam Technical Manual, 2013) and parametric analyses were carried out to investigate their effect on the structural response of the system. Findings Composite DELTA® beams can achieve fire resistances ranging from 120 to 180 min, depending on the depth and geometry of their cross-section, with deeper sections displaying a better fire response. The intense thermal bowing that occurs when these beams are heated from below has a more pronounced effect, in terms of thermally induced deflections for deeper sections. The satisfactory fire resistance of these beams is achieved due to the action of the concrete encased web and the reinforcement which compensate for the loss of the exposed lower flange. Increasing the thickness of the web in deeper sections improves their fire rating up to 180 min. The thickness of the lower flange affects the fire rating of the beams only in a minor way. Practical/implications The paper describes a numerical methodology to estimate the fire resistance of complex flooring systems.

Assessment Of The New Faliron Steam-electric Station In Greece

The New Faliron steam-electric station, the first one in Greece, is a listed historical building. The initial structure was constructed at the start of the 20 th century but a number of interventions followed until the 1960s. The structure was built with natural stone masonry, steel trusses and floors (with jack arches and joist fillers) and concrete floors reinforced with twisted cold formed rebars. The 12.5m high masonries practically lack any lateral restraints while large openings (doors, windows) exist. This paper presents brief information on the history of the structure, phases of construction, description of structure (dimensions, types of structural systems, etc), material properties and pathology. In addition, detailed information is presented regarding the assessment performed in accordance with the current code specifications (Eurocodes), including seismic actions. Especially for the masonry, a detailed finite element model was developed, whereas the seismic forces were evaluated through alternative methodologies (modal response spectrum analysis per EC8 and time history analyses). For the assessment of the RC part a displacement based methodology was applied as it is restrained by the surrounding masonry walls. From the assessment analysis, useful conclusions are drawn regarding the seismic performance of high masonry structures without lateral restraints and the behaviour of similar industrial structures under seismic effects.

Assessment and rehabilitation of the Volos municipal theater according to the Greek Retrofitting Code

The main objective of the present study is the assessment and retrofit of an existing reinforced concrete building. In particular, the study concerns the municipal theater of the city of Volos, Greece and it was carried out following the provisions and requirements of the Greek Retrofitting Code (KAN.EPE.), which adopts the Performance Based Design (PBD) concept. The theater was built during the 70s and was designed according to the Greek Royal Decrees of 1954 and 1959. The theater consists of the stage and the auditorium, which were analyzed independently, because they constitute two disjoint reinforced concrete (RC) structures. Their structural system consists of spatial frames and shear walls. The columns and the beams are simulated with beam elements with concentrated plasticity and the shear walls with equivalent diagonal truss elements which simulate the shear behavior of the wall structural element. Nonlinear static (Pushover) analysis is applied in order to estimate the seismic performance of the two structures for two performance objectives (A2 and B1 according to the provisions of KAN.EPE.). These correspond to the “Operational” and “Life Safety” performance levels for seismic hazard levels with a 50% and 10% probability of exceedance in 50 years, respectively. A retrofitting scenario is proposed for both the stage and the auditorium in order for the performance objectives to be met. It includes concrete jacketing of certain beams, columns and shear walls as well as strengthening of specific beams with fiber-reinforced polymers (FRPs).

Structural Appraisal of Two Steel Tanks Filled at Low Liquid Level

The object of this paper is to evaluate the structural adequacy of two existing large diameter steel tanks filled at low liquid levels by application of current design specifications. Emphasis is given on buckling of the circumferential shell and phenomena related to overall stability. Calculations according to the American standard API 650, which provides analytical expressions for determining overturning and sliding resistance as well as a design procedure for stiffening the shell against wind action, are presented. Simulation of the tanks via the finite element method, for obtaining the necessary shell stresses, was performed as required by the European standard EN1993-1-6. Based on the results, overall stability was checked and shell buckling was evaluated according to the “stress design” concept described in the aforementioned code. Differences in the results between the two standards are discussed and comments regarding their safety are made.