Untersuchungen und theoretische Modelle von druckbeanspruchten Stahlstützen in Verbundbauweise

Experimental and analytical modelling of steel columns reinforced by concrete encasement. Experimental investigations of steel‐concrete axially compressed columns that were tested in the Laboratory of the Institute of Building Structures of the Warsaw University of Technology are presented. The results of conducted experimental work created a basis for the detailed investigations into the appraisal of the influence of different factors associated with the behaviour of tested elements. Analytical modelling was done with use of the finite element method and the ABAQUS software. In the analysis, the emphasis was put on the influence of those factors that have the most important effect on strength and deformability of composite columns. As to the authors' knowledge, the investigated factors have not been accounted for accurately enough in current design codes. The factors such as the load application to the composite column end and the restraining conditions at the supports are among those most important from the design point of view. The investigations have a great practical aspect at this particular moment when in Poland there is an ongoing discussion associated with the proposed new national code on design of composite steel‐concrete structures. The said codification proposal is an attempt to harmonize the national design rules with those applied in the Eurocode 4. The experimental part was concerned with testing of 16 composite columns that were made as completely encased steel I‐type elements (HEA160 section used). The main sectional dimensions were 260 mm × 260 mm, and the column length – 2500 mm. In addition, the reference steel column of HEA160 section was tested. The parameters that were being changed during experiments consisted of the following ones: the way of the load application to the column end face, compressive strength of the concrete encasement and the restraining effect at the supports that reproduced that of assumed in the numerical studies. The behaviour of composite columns with fibre‐reinforced concrete heads was also investigated. The comparison of load deflection curves from the experiments and those from the computer modelling was carried out. In addition, failure loads from the laboratory tests were compared with those calculated according to some chosen design codes. The analysis carried out proven that both the way at which the load is applied to the element end face and the type of end restraints had a great influence on the strength of composite columns. It is clear from the experiments that in case of load application directly through the steel section, the attainment of the limit state of cracking was much earlier than the strength ultimate limit state, so that it controlled the design of composite columns. In this case, an increase in strain of steel sections was observed. In addition, the rigid restraining conditions at the column ends resulted in a decrease of the load bearing capacity because of the stress concentration in the concrete encasement within the support zones. The failure of composite columns was controlled by the combined stress state in the concrete encasement. The study carried out has shown that the load bearing capacity of composite columns can be substantially increased by the applications of fibre‐reinforced column heads at their end supports. The strength of such columns increased by 30–48% if compared with the same composite columns but made without fibre‐reinforced ends.     

Erforderliche Einspanntiefe von Stahlstützen in Betonfundamenten

Required length of restraint for steel columns in concrete foundations. Steel columns are connected frequently bending resistant to concrete substructures. With this type of construction the required length of restraint must be specified and the load‐carrying capacity of the steel columns within the range of the concrete foundations has to be verified. In the report consistent load‐carrying models are presented, which are considering the ultimate plastic load‐carrying capacity of cross sections and new calculation models according to Eurocode 3 for locals verifications. The verification conditions are formulated for steel columns made of rolled and welded I‐sections, which are stressed by one‐ or two‐axial bending with compression normal force. For columns with rolled sections calculation adds are given, which makes it possible to read off directly the required length of restraint.     

Drillknicken einfach‐symmetrischer Stahlstützen mit erzwungener Drehachse

Torsional buckling of mono‐symmetrical columns of steel structures with prescribed axis of rotation. Presented herein solution concerns the problem of elastic, spatial stability of mono‐symmetrical I‐columns of steel structures with prescribed axis of rotation placed in the plane of the cross‐sectional symmetry, parallel to the longitudinal axis. In association with it one‐bay columns with point elastic constraints, along the length, due to torsion and warping have been considered. The point's constraints have been taken into account model using a distributional calculus. The columns are loaded by the combined compressive force and bending moment, acting in the plane of the cross‐sectional symmetry. For the columns under constant bending moment the prob‐lem of stability has been solved in the closed form for the arbitr‐ary conditions of ends supporting. Whereas for columns under non‐uniform moment the solution has been obtained by the Bubnov‐Galerkin orthogonalization method for chosen conditions of the ends supports. The solutions have been depicted by calculations, in which the critical load of the elastic, torsional buckling has been determined for steel columns with prescribed axis of rotation. The computations have been executed by the help of an own software worked out on the basis of the introduced solutions. The experimental investigations carried out on I‐columns, braced laterally and longitudinally, under compression and bend‐ing, in order to determine their critical loads of elastic spatial buckling have been presented as well. These experimental inves‐tigations are to verify the theoretical solution derived by approximation method. General remarks and conclusions of practical nature have finished the work.     

Untersuchungen zur Homogenität von Bauwerksteilen mit Lasertechniken

Investigations concerning homogeneity of building parts by laser techniques. The subproject B1 “Diagnostics and Quality Control by Non‐Destructive, Contactless Testing Techniques” is working within the CRC 524 on the procedural and measurement technological evolutionary development of the conventional ultrasonic through‐transmission method towards an optical measuring method by application of laser technologies. The aim is the determination of the distribution of elastic characteristic parameters for the evaluation of laboratory test specimens in investigations on durability of concrete and for the actual state of construction elements in the course of revitalising buildings. In this case, a laser induced sound excitation takes place by means of an Nd:YAG‐laser. The sound waves that have been influenced by the investigation object are detected by a laser vibrometer. By applying these methods, both a high lasing rate and a high achievable data density are to be expected since the laser beams in both systems can be deflected optically by means of scanners. Furthermore, a surveying‐technological approach for sound path determination at each pair of measuring points has been developed, which can also be used for the conventional application of the ultrasonic through‐transmission method.     

Versuche zur Tragfähigkeit von Ankerplatten mit einbetonierten Kopfbolzendübeln in schmalen Stahlbetonstützen

Müssen große Lasten von Stahl‐ in Betonbauteile eingebracht werden, sind Ankerplattendetails mit aufgeschweißten Kopfbolzendübeln oft praktikable Lösungen. Dies gilt auch für die Befestigung von Stahlträgern an Stützen aus Stahlbeton. Hier können die Ankerplatten z. B. bauseits an der Schalung befestigt und mit dem Ortbeton einbetoniert werden. Die Dimensionierung dieser Einbauteile kann, wie auch die Berechnung von nachträglich installierten Befestigungsmitteln, derzeit nach Europäischen Technischen Zulassungen (ETA) erfolgen. Im Unterschied zu nachträglich installierten Befestigungen ist für die Ankerplatte mit einbetonierten Kopfbolzendübeln eine rechnerische Nutzung der Tragfähigkeit der Bewehrung möglich. Allerdings führen die diesbezüglichen Regelungen – im Vergleich zu den in den Versuchen ermittelten Tragfähigkeiten – rechnerisch zu stark eingeschränkten Tragfähigkeiten. Dies beruht einerseits auf der Reduktion der Tragfähigkeit wegen geringer Randabstände und andererseits auf der stark eingeschränkten Nutzbarkeit der Bewehrung. Im folgenden Beitrag werden Versuchsergebnisse vorgestellt, welche den Einfluss der Betondruckfestigkeit, der Verankerungslänge, der Lastexzentrizität sowie der Bewehrungsmenge und ‐position auf das Versagensgeschehen und die Tragfähigkeit zeigen. Results of Experimental Investigations on the Load‐Bearing Capacity of Steel Anchor Plates with in Concrete Encased Headed Studs in Reinforced Narrow Concrete Columns Anchor plates with welded shear studs are often used to transfer high loads from steel to reinforced concrete elements. This is for example the case for the fixation of steel beams to reinforced concrete columns. The anchor plates are fixed on site on the formwork and cast in‐place in the concrete. The design is calculated according to European Technical Approvals like the design of post‐installed anchors. In contrast to post‐installed fastenings, the utilisation of the reinforcement of in concrete encased headed studs is theoretically possible. But the regulations of the ETAs lead to great reductions in the analysed load‐bearing capacities compared to the capacities, obtained in tests. These tests have been conducted to investigate the load bearing behaviour and failure modes of anchor plates, especially in narrow reinforced concrete columns. In the following article the results of the experimental investigations are presented, which show the influence of concrete compression strength, shear stud length, load eccentricity as well as amount and position of reinforcement.     

Wölbkrafttorsion von Durchlaufträgern mit konstantem Querschnitt unter Berücksichtigung sekundärer Schubverformungen

Warping torsion of continuous beam with constant cross‐section considering shear deformation. The analogy between the theory of warping torsion and second order theory of a bending member with tensile force is also valid, if shear‐deformations in both cases are additionally included. On the basis of this analogy the three‐moment equation for continuous beam with constant cross‐section is given. It is demonstrated, that shear‐deformations for open sections can normally be neglected but must be encluded in the case of hollow‐sections. It is also shown, that for these sections warping‐torsion occurs only in ranges of discontinuity, but causes stresses which are in the same order as the stresses of primary torsion.     

Vergleichende Untersuchungen von Standard‐Klimadatensätzen (Testreferenzjahren) mit gemessenen Langzeit‐Klimadatensätzen für den Standort Kassel

Comparative study of standard sets of climate data (test reference years) with measured long‐term climate data for the location Kassel/Germany. For an inner‐city location in Kassel representative TRY (test reference year) data sets are compared with technical measurement results of long‐term climatic data especially as regards their application for the simulation of a building's thermal performance. This research study was carried out on the basis of climate measurements which were recorded over the period from 1994 to 2003 by the climate station of the building physics department at the University of Kassel. Both the analysis of the mean temperature values and that of the excess‐temperature degree hours show, that the test reference year in summer comprises considerably lower outside temperatures than the 10‐years average of the measurements. Not only the test reference standard year but also the data set of the German Meteorological Service for an extremely warm summer proved to be not representative. For winter, the standard year reflects the average measured conditions quite well. The outside temperature of the test reference year for a “cold winter”, however, lies well below the values of the coldest measuring periods in January and February. The comparison of simulation results with various sets of climatic data shows that deviations in the sets of climatic data also lead to clear differences in the computed values of temperature conditions in summer and in the heating energy requirement. The decade from 1990 to 2003, as is known, is one of the warmest decades since the beginning of weather recording. Whether the deviations described are due to this or rather to the very different topography of the reference location by comparison with the measuring station cannot be clarified on the basis of this investigation, presumably there is an interaction of both influences. The research study quantitatively shows, however, the range of error which may result from the application of reference climatic data.     

Untersuchungen zur Tragfähigkeit von geschädigten Spanngliedern mit nachträglichem Verbund

Investigations on the Ultimate Strength of Damaged Post‐Tensioned Tendons In order to assess the influence of bond action between strands, injection grout and surrounding concrete on the ultimate strength of damaged post‐tensioning tendons more accurately, a series of tensile tests on tendons which were built using post‐tensioning strands and wires from demolished bridges were carried out. Wire and strand breakage was included in the tendons at specified patterns. Furthermore, the influence of the quality of the injection grout on the load carrying‐capacity of the tendon was studied. The results of the test series show that tendons with damaged or broken wires or strands are able to carry a high percentage of the ultimate load of an undamaged tendon.     

Elasto‐plastische Schubverformungen und Schubversagen kurzer Stahlstützen

Elasto‐plastic shear deformation and fracture behaviors of short steel stanchions. Short steel stanchions with various width‐to‐thickness ratios of flange and web under axial compression are clarified experimentally as well as analytically. There exists a critical value of shear span ratio _Gr(H/h) between shear and bending yield of wide flange steel stanchions. Shear yielding of short steel columns shows no Lüders's lines but very many small protuberance particles up to parallelogram deformed web surfaces. There exists a fundamental large difference between shear and bending yield behaviors of wide flange steel stanchions. Finally the critical shear span ratio of wide flange steel profile will be derived analytically and through experiment proved.