Nichtlineare Analyse der zeitlichen Antwort von Stahlbeton‐, Spannbeton‐ und Verbundkonstruktionen auf die mechanische Einwirkung und Temperatureinwirkung

Nonlinear Analysis of the Time‐Dependent Response of Reinforced and Prestressed Concrete Structures to Mechanical and Temperature Loads The developed computational procedure for the nonlinear analysis of the time‐dependent response of structures to mechanical loads and to elevated temperature in fire up to failure is limited to plane frame structures. They can be carried out as reinforced or prestressed concrete structures or as steel‐concrete composite structures. The analysis takes into account all types of structural nonlinearities, resulting from the geometry of the structure and from the material properties, including rheology. The computational procedure for the analysis is based on the finite element method. A highly effective finite element P4 is used. Its curvature along the element axis is interpolated using fourth order polynomial. The stress‐strain state of the structure is analysed gradually and iteratively according to the time intervals. The nonlinear equation systems of the structure are solved numerically using the Newton‐Raphson procedure.     

Instandsetzung und Verstärkung von Stahlbrücken mit Kategorie‐3‐Schäden

Reinforcing steel bridges with category 3 damages – report on a BASt research project. In recent years, fatigue damages have been observed at the main supporting structure of steel bridges, the orthotropic decks, as well as the transverse structure of steel bridges (the so‐called category 3‐failure). The rapidly increasing road traffic intensifies the situation resulting in a huge amount of steel bridges affected by fatigue damages. Existing steel bridges with category 3‐fatigue cracks have been intensively investigated. Fatigue failure modes and general evaluation criteria have been summarized, analysed and categorized, in order to enable first fundamental and time‐efficient definition and classification of category 3‐damages. FE‐simulations of transversal steel bridge structures (with and without reinforcements) have been carried out to evaluate and review the structural bridge concepts. Based on these studies, a special way of the steel bridges' maintenance has been followed up, which is removing all possible transversal bracings. Finally, different options of maintenance and repair have been investigated both newly and successfully applied in the recent past. Appropriate actions for solving essential category 3‐fatigue problems are presented.     

Life‐cycle cost assessment of mid‐rise and high‐rise steel and steel–reinforced concrete composite minimum cost building designs

The traditional trial‐and‐error design approach is inefficient to determine an economical design satisfying also the safety criteria. Structural design optimization, on the other hand, provides a numerical procedure that can replace the traditional design approach with an automated one. The objective of this work is to propose a performance‐based seismic design procedure, formulated as a structural design optimization problem, for designing steel and steel–reinforced concrete composite buildings subject to interstorey drift limitations. For this purpose, eight test examples are considered, in particular four steel and four steel–reinforced concrete composite buildings are optimally designed with minimum initial cost. Life‐cycle cost analysis (LCCA) is considered as a reliable tool for measuring the damage cost due to future earthquakes that will occur during the design life of a structure. In this study, LCCA is employed for assessing the optimum designs obtained for steel and steel–reinforced concrete composite design practices. Copyright © 2011 John Wiley & Sons, Ltd.     

Dauerhaftigkeit der Verschlüsse von Schleusen und Wehranlagen

Durability of the gates of locks and weir plants. Hydraulic steel constructions are special steel structures. They have a high relevance for the operability and bearing capacity of a water‐structural plant and are subject to special requirements and operating conditions. Therefore high demands are made on their durability. Due to the immersion medium “Water” the steel structures of the gates of shiplocks and movable weirs are exposed to corrosion hazards exceedingly. Gates of ship locks are stresses by fatigue additionally. Concerning the steel structures of weirs corrosive, abrasive and/or hydrodynamic effects dominate. An overview will be given which methods and possibilities are used to achieve an appropriate durability during the intended service life under these circumstances. In this context the importance of a regular structure‐maintenance will be shown too. Furthermore new innovative gate structures may offer advantages with regard to fatigue strength, simplified maintenance and inspection possibilities and favorable corrosion protection characteristics.     

Direct displacement‐based design of steel‐braced reinforced concrete frames

This study investigates a direct displacement‐based design procedure for dual system structures composed of reinforced concrete frames and steel bracings. In this procedure, in order to establish the design displacement profile before any analysis, strength proportions between bracings and frames are assigned. By using the displacement profile and damping characteristics of the structural components, the structure can be represented as an equivalent single‐degree‐of‐freedom system. The effective period and secant stiffness of the structure are then calculated, and finally, after the base shear was computed, the design process can be implemented. Structures with 4, 8 and 12 stories have been designed using this methodology, and in order to validate it, seven accelerograms have been used for nonlinear time‐history analysis of the above structures. The results demonstrate the efficiency of this procedure. Copyright © 2012 John Wiley & Sons, Ltd.     

Die Geh‐ und Radwegbrücke Kehl – Strasbourg

The Pedestrian and Cycle Bridge Kehl – Strasbourg. The Rhine bridge between Kehl and Strasbourg is the new regional landmark and linking element of the International Gardening Show. The approach to unifying different functions and an architectural endeavour lead to a unique structural system. Two separate decks address the different situations on the river banks and, linked by a platform, form a balcony above the Rhine at midspan. The main bridge is a cable‐stayed structure with a steel pylon and a steel‐concrete composite deck. The approach bridges are continuous girders on steel columns. Both pile and flat foundations are featured in the design. The article describes the structural concept and design, outlines the erection procedure and discusses aspects of the dynamic behaviour of the bridge.     

Numerisches Verfahren zur Optimierung von ebenen Stahlfachwerkträgern

Numeric method to optimise two‐dimensional trussed girder. A numeric method for weight optimisation of two‐dimensional steel trussed girder will be introduced. Two parameters, the cross‐section and the height of framework, are to be changed by iteration until the minimal weight of structure is optimized. A height‐weight‐figure presents the obtained information on geometry und material consumption. The information will support the structural engineer during the first steps of construction design. Due to economic and ecological reasons the optimisation of structure‐weight will be of utmost importance in the designing process.     

Behavior of coupled shear walls with buckling‐restrained steel plates in high‐rise buildings under lateral actions

Traditional coupling beams in coupled shear walls (CSWs) may be lack of required ductility or inconvenient to be fully repaired or replaceable after earthquake damage. To improve the CSW seismic performance, a type of new structural system, which is referred to as coupled shear walls with buckling‐restrained steel plates (CSW–BRSP), is proposed and thoroughly studied. In the system, a pair of individual concrete wall is coupled through buckling‐restrained steel plates instead of traditional concrete coupling beams. Based on the continuous medium method (CMM), stiffness and strength design formulas are developed for the seismic design of this system. Intensive investigations have been conducted to assess the undesirable axial forces in the buckling‐restrained steel plates induced by lateral loads. In order to facilitate the application of this system, a detailed design procedure is also explicitly stated. Finally, an example of typical high‐rise building is presented to illustrate the design procedure as well as demonstrate the excellent seismic performance of the proposed system by means of nonlinear time‐history analysis. Copyright © 2015 John Wiley & Sons, Ltd.     

Numerische Analyse geschweißter Verbindungen von Duplexstahl und Quarzglas

Numerical analysis of welded joints between duplex steel and quartz glass. Welded joints are a vital element in structural engineering. Originating from conventional carbon steel welding in construction, recent advancements in welding technology now allow the joint of modern high‐strength steel and glass materials. With today's methods, an analysis of the welded joints' structural behaviour can be conducted by experiment, as well as by numerical analysis. Particularly for the numeric analysis, capturing the non‐linear thermal and mechanical properties of the materials is important, in order to allow a realistic determination of temperature, microstructure and residual stresses for different types of joints. Simulations of multi‐layered weld joint on duplex steel show, that a targeted heat treatment during MAG‐welding by variation of the welding parameters achieves a beneficial ratio between ferrite and austenite which, for example, ensures a high resistance of the weld to corrosion. The material quartz glass can generally be welded as butt‐weld with a CO₂‐laser. The simulations of a welded joint of a plate and a pipe show, that an optimization of the welding technology of preheat laser beam and welding laser beam is necessary, in order to reduce the thermal impact during the welding process, as well as residual stress in the joint. At the Department of Steel Structures at the Bauhaus‐Universität Weimar, numerical simulations of welded joints between steel and glass materials are a current and topical research focus.     

Ausgewählte Versuchsergebnisse und Erkenntnisse zum Tragverhalten von Stäben aus I‐ und U‐Profilen

Some test results and cognitions on structural behaviour of I‐ and U‐beams. Within the scope of a research project extensive experimental and theoretical investigations concerning the load‐carrying capacity of hot‐rolled profiles have been performed by the institutes for steel construction of the universities of Aachen, Berlin and Bochum [1]. Five of the 70 conducted tests were se‐lected in order to report in detail on them in the present article. By means of collateral calculations effects on the structural behaviour and the load‐carrying capacity are clarified. The achieved cognitions are evaluated and explained with regard to the practical design experience.     

Zur Leistungsfähigkeit,korrekten Anwendung und Kontrolle von EDV‐Programmen für die Berechnung räumlicher Stabwerke im Stahlbau (Teil 1)

On performance, correct use and control of computer programs for structural analysis of three‐dimensional steel frameworks. Structural analysis of three‐dimensional steel frameworks is normally carried out by means of computer programs based on second or higher order theory. The present article classifies under special consideration of equivalent imperfections, whether these simplified theories are adequate or if additional terms are necessary to obtain sufficiently accurate results in practical engineering in any case. For software producers and users, several simple examples are presented, in order to demonstrate the general performance of a software. Furthermore important hints are given for the correct use of computational software developed for statical framework calculation.     

Aktualisierte Diagramme zur Bemessung von Stahlkonstruktionen für den Brandfall nach Eurocode 3

Updated diagrams for fire design of steel structures based on Eurocode 3. The forthcoming design methods for steel structures subjected to fire in Eurocode 3 [1] differ considerably from the methods in the current German standard DIN 4102. The required fire protection material cannot be specified by simplified tables any longer. The structure will now be designed for the case of fire like it is done for ambient temperature. With this method the cost‐intensive structural fire protection can be optimized or even be avoided. However, the more realistic design comes along with a higher effort of calculation. To minimize this effort, in [3] a design tool was developed and published in [4]. In this tool the design methods of the Eurocode have been diagrammed for simple use. However, it is based on the prestandard and cannot be used any longer due to some changes in the current Eurocode. Therefore updated diagrams are presented and further diagrams are added to reduce the calculation effort for the design of steel structures in fire as much as possible.     

Drift design of steel‐frame shear‐wall systems for tall buildings

Drift design methods based on resizing algorithms are presented to control lateral displacements of steel‐frame shear‐wall systems for tall buildings. Three algorithms for resizing of structural members of the steel‐frame shear‐wall systems are derived by formulating the drift design process into an optimization problem that minimizes lateral displacement of the system without changing the weight of a structure. During the drift design process, cost‐effective displacement participation factors obtained by the energy method are used to determine the amount of material to be modified instead of calculating sensitivity coefficients. The overall structural design model with the drift design method for the steel‐frame shear‐wall systems is proposed and applied to the structural design of three examples. As demonstrated in the examples, the lateral displacement and interstorey drift of a frame shear‐wall system can be effectively designed by the drift design method without the time‐consuming trial‐and‐error process. Copyright © 2002 John Wiley & Sons, Ltd.     

Erweiterung der DASt‐Richtlinie 009 für die Stahlgütewahl bei Einschubverbindungen im Hochbau

Extension of DASt‐RiL 009 for the choice of steel quality for welded connections of bracing components in building constructions. DASt‐Richtlinie 009, equivalent to DIN EN 1993‐1‐10, provides a tool based on fracture mechanics for the choice of material of steel structures to avoid brittle fracture at low temperatures. The procedure has initially been developed for the conditions of bridges, i.e. for fatigue loading and is applicable for all structural details for which fatigue classes are determined in DIN EN 1993‐1‐9 or in DIN‐Fachbericht 103. For such structural details the procedure can also be applied for buildings on the safe side. Economic connections in building frames, e.g. welded connections of bracing components in slotted gusset plates are normally designed with plastic resistance models ignoring any notch effect relevant for fatigue. Therefore they are not in the scope of DASt‐RiL 009. This contribution gives a proposal for an extension of DASt‐RiL 009, such that it covers these types of connections in building frames as well. The procedure of determining tables for the selection of steel qualities is as for bridges, except that the assumptions for the assessment (e.g. crack sizes) are different. The simplified tables have the same format as table2 in DASt‐RiL 009, however the influence of plate thickness is smaller than that of other geometric parameters.     

Ermüdungsverhalten von Mobilkranbauteilen aus hochfesten Baustählen

Fatigue behaviour of component sections of mobile cranes out of high strength steel plates. High‐strength structural steels with 960 and 1100 MPa minimum yield strength allow a decrease of the investment and operating costs of mobile cranes through lightweight design. However, there still exists an uncertainity for stress resistance under cyclic loads and bearable stresses concerning fatigue behaviour of important crane components. This paper deals for the first time with the fatigue behaviour of crane components examined under realistic load‐time‐cycles derived from realistic crane operating conditions. The results supply important information as they indicate that the service life for both steels, even with very high applied stress, is at least 20years. Moreover, it is shown that further improvements of the durability are possible around up to 50% through subsequent treatment of the welds, toughness improvement of the base material and constructive remodelling of the components. Additionally, this paper provides a new design method with which the fatigue behaviour of crane components under most different aspects and involved variable combinations can be estimated, consistent with measured values, through a fracture mechanically based model. Important procedure recommendations and hints can be given for a more intense use of high‐strength structural steels for practical application in mobile crane engineering. Inspection intervals and contents can be newly determined.     

Numerische Simulation des Verhaltens von Betontragwerken unter Brandeinwirkung

Numerical Simulation of the Response of Fire Exposed Concrete Structure The proposed numerical model for concrete and reinforced concrete structures subjected to fire comprises the transient thermal and mechanical analysis considering the temperature dependent material properties of concrete and reinforcing steel within the framework of the phenomenological approach of the Eurocode 2, part 1‐2. A concrete model, based on the combination of plasticity and damage theory, serves as the basis for the material model of concrete for high temperatures. For reinforcing steel a standard elastic‐plastic material model is employed. The proposed model is validated by the numerical simulation of fire tests on plain concrete specimens and by the numerical simulation of a large scale fire test on a reinforced concrete slab. Furthermore it is used to determine the structural integrity of a tunnel structure, put up by the cut‐and‐cover method, exposed to fire.     

Performance‐based plastic design and collapse assessment of diagrid structure fused with shear link

A diagrid structure fused with shear link (DSSL) is an innovative earthquake resilient structural system. The DSSL combines the steel diagrid structural system with shear links to dissipate the earthquake energy with the goal to minimize structural repair and downtime after strong earthquake shaking. The SLs are placed between diamond‐shaped grid units and decoupled from the gravity system. To facilitate the design of the proposed DSSL system, the performance‐based plastic design (PBPD) procedure is extended to design a prototype building utilizing DSSL. Detailed finite element model is developed to simulate the non‐linear dynamic response of the structure under a range of earthquake shaking intensities. The results of non‐linear dynamic analyses show that the DSSL has excellent seismic performance and can be efficiently designed using PBPD. Lastly, detailed collapse risk assessment of the prototype building is performed using the FEMA‐P695 methodology. The result shows that the PBPD‐designed DSSL has adequate margin against collapse. Hence, it can be used as an effective seismic force resisting system.     

Integrated wind‐induced response analysis and design optimization of tall steel buildings using Micro‐GA

This paper presents an integrated procedure for wind‐induced response analysis and design optimization for rectangular steel tall buildings based on the random vibration theory and automatic least cost design optimization technique using Micro‐Genetic Algorithm (GA). The developed approach can predict wind‐induced drift and acceleration responses for serviceability design of a tall building; the technique can also provide an optimal resizing design of the building under wind loads to achieve cost‐efficient design. The empirical formulas of wind force spectra obtained from simultaneous measurements of surface pressures on various rectangular tall building models in wind tunnel tests are verified testified using a published example. Upon the known wind force spectra, the equivalent static wind loads for every storey, such as along‐wind, across‐wind and torsional loads, are then determined and applied for structural analysis including estimation of wind‐induced responses. An improved form of GAs, a Micro‐GA, is adopted to minimize the structural cost/weight of steel buildings subject to top acceleration and lateral drifts constraints with respect to the discrete design variables of steel section sizes. The application and effectiveness of the developed integrated wind‐induced response analysis and design optimization procedure is illustrated through a 30‐storey rectangular steel building example. Copyright © 2009 John Wiley & Sons, Ltd.     

Equivalent viscous damping in direct displacement‐based design of steel braced reinforced concrete frames

Performance‐based design method, particularly direct displacement‐based design (DDBD) method, has been widely used for seismic design of structures. Estimation of equivalent viscous damping factor used to characterize the substitute structure for different structural systems is a dominant parameter in this design methodology. In this paper, results of experimental and numerical investigations performed for estimating the equivalent viscous damping in DDBD procedure of two lateral resistance systems, moment frames and braced moment frames, are presented. For these investigations, cyclic loading tests are conducted on scaled moment resisting frames with and without bracing. The experimental results are also used to calibrate full‐scale numerical models. A numerical investigation is then conducted on a set of analytical moment resisting frames with and without bracing. The equivalent viscous damping and ductility of each analytical model are calculated from hysteretic responses. On the basis of analytical results, new equations are proposed for equivalent viscous damping as a function of ductility for reinforced concrete and steel braced reinforced concrete frames. As a result, the new equation is used in direct displacement‐based design of a steel braced reinforced concrete frame. Copyright © 2012 John Wiley & Sons, Ltd.