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Mirambell, Enrique; Bordallo, Jordi; Real, Esther  Torsion and its interaction with other internal forces in EN 199311  a new approach  Steel Construction  3/2016  240248  Articles 
KurzfassungThis paper presents and clarifies the treatments included in EN 199311 [1] relating to checking the resistance of steel crosssections under torsion and its interaction with other internal forces. Specifically, the origin of the formulations for sheartorsion interaction, which has not been found in the literature, is presented. Furthermore, a very simple formulation based on the expressions used for sheartorsion interaction is developed in order to take into account bendingwarping torsion interaction for symmetrical Isections (IP and HE steel profiles). Such a formulation overcomes the overly conservative approach given in EN 199311 [1] for class 1 and class 2 crosssections (plastic and compact crosssections). Finally, a rigorous method for determining the bending resistance of crosssections is proposed considering the interaction with shear and torsion. The proposal is well suited to the concept of crosssection class and is perfectly consistent with the approaches set out to consider bendingshear and bendingwarping torsion interactions. x


Helbig, Thorsten; Riederer, Jochen; Kamp, Florian; Oppe, Matthias  Freeform on every scale  "Tornado" roof structure for Bory Mall, Bratislava, Slovakia  Steel Construction  3/2016  249354  Reports 
KurzfassungThe Bory Mall Shopping Centre, designed by the Italian architect Massimiliano Fuksas, is a mixed use development located on the outskirts of Bratislava, Slovakia. x


World Steel in Figures 2016 is available  Steel Construction  3/2016  254  News  
Schueremans, Luc; Furtado, Ana Claudia  FRISOMAT  steel innovator in coldrolled buildings  Steel Construction  3/2016  255258  Reports 
Euro Space Center at LibinTransinne  Steel Construction  3/2016  258  News  
ECCS news: Steel Construction 3/2016  Steel Construction  3/2016  259263  ECCS news  
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Announcements: Steel Construction 3/2016  Steel Construction  3/2016  264  Announcements  
Contents: Structural Concrete 3/2016  Structural Concrete  3/2016  Contents  
Hordijk, Dick  Old and new meet at the 2017 Maastricht fib Symposium!  Structural Concrete  3/2016  307308  Editorials 
von GreveDierfeld, Stefanie; Gehlen, Christoph  Performance based durability design, carbonation part 1  Benchmarking of European present design rules  Structural Concrete  3/2016  309328  Technical Papers 
KurzfassungThe paper reports on a benchmark of European deemedtosatisfy rules for exposure class XC (carbonation exposed structural members). The benchmark of the descriptive rules was carried out following the probabilistic design approach for carbonationinduced corrosion developed in [1] and adopted in fib bulletin 34: Model Code for Service Life Design (2006) [2] and fib Model Code for Concrete Structures 2010 [3], respectively. To perform a representative study, three groups of European countries were selected, representing different parts of Europe, south (Spain, Portugal), middle (Netherlands, Great Britain and Germany) and northern Europe (Denmark, Norway). Reliability ranges for carbonationinduced depassivation of rebar were calculated for “favourable” and “unfavourable” design situations in exposure classes XC2, XC3 and XC4 [4]. In each design situation the deemedtosatisfy rules of selected countries were followed. The probabilistic calculations were mainly based on shortterm carbonation data. However, some calculations were also based on longterm observation. The latter was implemented for independent validation purposes. The calculated reliability ranges are very broad and in some “unfavourable” situations, the deemedto satisfy requirements do not guarantee the required limit state (LS) arget reliabilities for the particular exposure. In “favourable” situations less stringent demands would have been sufficient. x


Gehlen, Christoph; Osterminski, Kai; Weirich, Tim  Highcycle fatigue behaviour of reinforcing steel under the effect of ongoing corrosion  Structural Concrete  3/2016  329337  Technical Papers 
KurzfassungThis paper presents the results of the corrosion fatigue behaviour of profiled reinforcing steel bars. Cyclically loaded rebar was simultaneously exposed to different corrosive environments  moderate to severe corrosive environments simulating XC or XD/XS exposure. Corrosion was configured naturally without any external polarization. Rebar was exposed to the corrosive solutions either directly or, when embedded in concrete, indirectly. In this latter case, corrosive agents penetrated towards the steel surface through an open crack. Low frequency was applied to enable extended corrosion periods. The potential drop method was utilized to detect and quantify the crack initiation and crack growth of the rebar. Using this method it was possible to determine the ratios between the number of cycles to crack initiation and the cycles to failure. Based on this method, the Nini/NF ratios were almost always between 0.8 and 0.9  values that are similar to ratios determined for rebar tested in air (reference). This indicates that the fatigue life of rebar in carbonated concrete or concrete containing chloride is strongly dependent on crack initiation and less on crack growth. The SN curves derived from the corrosion fatigue tests deviate significantly from the curve that was measured during the reference fatigue tests (tests in air). The SN curves of rebar tested under corrosion fatigue load were linear, with a slope that was much steeper than the slope of the reference rebar tested in air. x


Prudente dos Santos, JoÃ£o Pedro de Oliveira Dias; CrÃ©mona, Christian; Campos da Silveira, AntÃ³nio Paulo; de Oliveira Martins, LuÃs Calado  Realtime damage detection based on pattern recognition  Structural Concrete  3/2016  338354  Technical Papers 
KurzfassungStructural health monitoring (SHM) can be defined as the process of developing and implementing structural damage detection strategies. Ideally, this detection should be carried out in realtime before damage reaches a critical state and impairs structural performance and safety. Hence, it must be based on sensorial systems permanently installed on the target structures and on fully automatic detection methodologies. x


Zhao, Yuxi; Zhang, Dawei; Shen, Shijun; Ueda, Tamon  Axial loading capacity of concretejacketed RC columns with pre and postcorrosion damage  Structural Concrete  3/2016  355364  Technical Papers 
KurzfassungThe main objective of this study is to investigate the effect of pre and postjacketing corrosion and loading damage on concretejacketed reinforced concrete (RC) columns under uniaxial loading and to develop a methodology for predicting the corresponding compressive strength. The pre and postdamage involved preloading up to 50 % of the peak load of the core column, an electrochemical process to accelerate the migration of chlorides from an external electrolyte into the test columns and a wettingdrying cycle process with a controlled current to speed up the corrosion of the steel reinforcing bars in the test columns. Uniaxial loading tests were performed to determine the structural performance of the concretejacketed columns with and without corrosion damage. The failure mode and loaddisplacement and loadstrain responses of the test columns were recorded, and the related mechanisms are discussed. A model capable of evaluating the compressive strength of unjacketed or jacketed RC columns with and without corrosion damage was then developed. The analytical approach considered the effect of reinforcement corrosion on the effective loadbearing area of the concrete and the confinement effect of the stirrups. The analytical results agree well with the experimental results, indicating the reliability and effectiveness of the models developed. x


Debernardi, Pier Giorgio; Taliano, Maurizio  An improvement to Eurocode 2 and fib Model Code 2010 methods for calculating crack width in RC structures  Structural Concrete  3/2016  365376  Technical Papers 
KurzfassungThe analysis of the mechanical behaviour of a reinforced concrete tie subjected to a monotonic loading in the stabilized cracking stage is performed here by way of a theoretical general model that considers the effect of the socalled Goto cracks (secondary cracks). It is shown, in particular, that the average bond stress along the transmission length depends not only on the concrete strength as assumed by the fib Model Code for Concrete Structures 2010, but also on reinforcement ratio and bar diameter. In this regard, tabulated theoretical values of the average bond stress are proposed as a function of the aforementioned parameters. Moreover, the secondary cracks reduce the effect of tension stiffening on the relative mean strain. On the basis of the main results obtained with the general model, some improvements are suggested for the calculation methods proposed by fib Model Code 2010 and Eurocode 2 concerning the average value of the bond stress and taking into account the influence of the secondary cracks on the mean deformation. An improved calculation method is therefore performed. Finally, the theoretical results of crack spacing and crack width obtained with the general and improved methods are compared with experimental data obtained from extensive research on RC ties. x


Visintin, Phillip; Oehlers, Deric J.  Mechanicsbased closedform solutions for moment redistribution in RC beams  Structural Concrete  3/2016  377389  Technical Papers 
KurzfassungWhen it comes to the efficient design of reinforced concrete beams and frames, moment redistribution is used to: reduce the absolute maximum magnitude of the moment in the critical region, equalize the critical moments on either side of interior columns and fully utilize the capacity of the noncritical regions of a member. Although important, historically, moment redistribution has proved to be difficult to quantify due to the complexity of quantifying hinge rotations. Although numerous empirical expressions exist for plastic hinge lengths, i.e. the length over which the ultimate curvature can be integrated in order to give hinge rotations, a comparison with a global dataset yields poor results. Using a recently developed mechanicsbased momentrotation approach, it is possible to quantify the momentrotation characteristics of reinforced concrete hinges. In the tension region, the approach applies partial interaction theory directly to simulate the mechanisms associated with slip of the reinforcement relative to the surrounding concrete as cracks widen, whereas in the compression region, partial interaction shearfriction theory is used to describe the formation and failure of concrete softening wedges. It is shown how the momentrotation approach explicitly allows for the size dependency. Furthermore, mechanicsbased solutions for moment redistribution are then derived and it is shown how these can be simplified at the ultimate limit state for use in the design office. x


di Prisco, Marco; Martinelli, Paolo; Dozio, Daniele  The structural redistribution coefficient KRd: a numerical approach to its evaluation  Structural Concrete  3/2016  390407  Technical Papers 
KurzfassungStructures made of a material with a very high standard deviation, such as fibrereinforced concrete, exhibit an exceptionally safe prediction of the maximum bearing capacity when this is derived from characteristic values identified by means of small specimens. This is emphasized when the structures are characterized by high redundancy. In this regard, two reference tests representing two extreme situations are considered: a) simply supported unnotched fullscale beams characterized by a statically determinate loading scheme and b) fullscale slabs on the ground characterized by a statically indeterminate loading scheme. The Italian standard and, more recently, the fib Model Code for Concrete Structures 2010 have introduced a coefficient (structural redistribution factor) that is able to take into account the reduced variability of mechanical bearing capacity when associated with a large volume involved in the failure process and/or when the structure is able to redistribute stresses significantly, thus favouring the average rather than the minimum strength. A numerical procedure taking into account the expected heterogeneity of the mechanical characteristics in the structure is introduced for the first time to evaluate the redistribution factor. x


Atta, Ahmad; Zaher, Fahmy; Etman, Emad  Structural performance of continuous RC slabs strengthened in negative moment regions with a mineralbased composite  Structural Concrete  3/2016  408424  Technical Papers 
KurzfassungAn experimental programme was proposed and carried out to assess the effectiveness of the mineralbased composite (MBC) technique for the flexural strengthening of negative moment regions in continuous reinforced concrete slabs. In addition to the testing of the two reference specimens, the experimental programme included the testing of nine continuous RC slab specimens with different strengthening techniques, namely, using ordinary steel bars and MBC material. This experimental programme was conducted to study the failure modes, the loaddeflection behaviour and the failure loads. x


D'Antino, Tommaso; Triantafillou, Thanasis C.  Accuracy of designoriented formulations for evaluating the flexural and shear capacities of FRPstrengthened RC beams  Structural Concrete  3/2016  425442  Technical Papers 
KurzfassungFibrereinforced polymer (FRP) composites have been employed in the last few decades largely for the strengthening and seismic retrofitting of existing reinforced concrete (RC) structures. Several studies are available in the literature and different analytical models have been proposed for evaluating the FRP contribution in strengthened RC elements. This paper analyses the accuracy of analytical models widely used for evaluating the flexural and shear contributions provided by the FRP. Some of those models are included in design guidelines. In particular, the analytical models for evaluating the FRP strain at intermediate crackinduced debonding failure are analysed. The accuracy of each formulation is assessed comparing the analytical provisions with the experimental results collected from two databases, one for bending and one for shear. The results obtained show that most of the analytical flexural models achieve a good level of accuracy and only a few models provide inadequate results. A new formulation proposed for evaluating the FRP shear contribution is shown to be generally conservative, which comes at the expense of accuracy. x


Lee, Deuck Hang; Han, SunJin; Kim, Kang Su  Dual potential capacity model for reinforced concrete beams subjected to shear  Structural Concrete  3/2016  443456  Technical Papers 
KurzfassungThe shear resistance mechanisms of a reinforced concrete (RC) member with shear reinforcement can be divided into the contributions of the concrete and the shear reinforcement. The shear resistance mechanisms of concrete can be further divided into the shear resistance of the intact concrete in the compression zone, the aggregate interlock in the cracked tension zone and the dowel action of the longitudinal tension reinforcement. The shear demand curves and potential shear capacity curves for both tension and compression zones have been derived in this study, with the assumption that the shear failures of RC members are dominated by the flexuralshear strength. The shear capacity model was also proposed on this basis. In the proposed model, the crack width and the local stress increase in reinforcement were calculated based on the bond behaviour between the reinforcement and its surrounding concrete. Further, the crack concentration factor was introduced to consider the formation and propagation of the critical shear crack that developed from the flexural cracks. The results of a total of 1, 018 shear tests were collected and compared with the analysis results provided by the proposed model. It was demonstrated that the proposed model provides a good estimate of the shear strengths of RC beams. x


Ricker, Marcus; Siburg, Carsten  Punching shear strength of flat slabs  critical review of Eurocode 2 and fib Model Code 2010 design provisions  Structural Concrete  3/2016  457168  Technical Papers 
KurzfassungThe fib Model Code for Concrete Structures 2010 introduces a new design concept for punching shear based on critical shear crack theory. This paper presents and provides the background to the design provisions for punching shear according to fib Model Code 2010, Eurocode 2 and the corresponding German National Annex to Eurocode 2. The different punching shear design provisions are critically reviewed by means of parameter studies and a comparison of the calculated resistances and test results. The safety levels of the code provisions are verified and the influence of the different punching parameters on the calculated resistances is examined in detail. x


Oviedo, Rodrigo; GutiÃ©rrez, Sergio; Santa MarÃa, HernÃ¡n  Experimental evaluation of optimized strutandtie models for a dapped beam  Structural Concrete  3/2016  469480  Technical Papers 
KurzfassungStrutandtie modelling constitutes a powerful tool for the design of complex structural reinforced concrete elements. It has been proved numerically that strutandtie (ST) models obtained using structural optimization methods produce designs that are more efficient. However, to the best of the authors' knowledge, no experimental evidence of such results has been published. This paper presents experimental results for nine test specimens; five of them were designed using optimal models derived from a full homogenization structural optimization algorithm, and the remaining four using conventional ST models for comparison purposes. Although all specimens carry loads higher than the factored design load, specimens based on ST models derived using full homogenization with reinforcement parallel to the ties exhibit better structural performance regarding crack growth control, more ductile modes of failure and a greater increase in load capacity. x


Herfelt, Morten A.; Poulsen, Peter N.; Hoang, Linh C.; Jensen, Jesper F.  Numerical limit analysis of keyed shear joints in concrete structures  Structural Concrete  3/2016  481490  Technical Papers 
KurzfassungThis paper concerns the shear capacity of keyed joints that are transversely reinforced with overlapping Ubar loops. It is known from experimental studies that the discontinuity of the transverse reinforcement affects the capacity and the failure mode. However, to the best knowledge of the authors, previous theoretical works and current design equations in standards do not account for this important effect. This paper introduces a detailed model based on finite element limit analysis to assess the effect of the discontinuous reinforcement. The model is based on the lower bound theorem and uses the modified MohrCoulomb yield criterion, which is formulated for secondorder cone programming. The model provides a statically admissible stress field as well as the failure mode. Twentyfour different test specimens were modelled and the calculations compared with the experimental results. The results of the model show satisfactory agreement with the experimental observations. The model produces estimates of the shear capacity that are significantly better than those of the Eurocode 2 design equations. x


Zhou, LinYun; Liu, Zhao  Investigation of the buckling behaviour of thinwalled hollow concrete piers  Structural Concrete  3/2016  491501  Technical Papers 
KurzfassungTall hollow concrete piers with high widthtothickness ratios are commonly used in longspan box girder bridges. Such thinwalled structures present the possibility of failure due to local buckling. So, in common practice, diaphragms are usually included in hollow piers to improve the local stability; however, is that necessary? Although experimental research on the buckling behaviour of hollow piers has been conducted extensively, few analytical attempts have been performed to reveal the effects of the widthtothickness ratio on local buckling behaviour. To this end, an analytical model has been proposed to investigate the local buckling behaviour of hollow piers. Following the RitzTimoshenko method, an analytical formula for critical local buckling stress has been developed and verified to have good accuracy compared with finite element analyses. Based on the buckling failure mode of a hollow pier with a slenderness ratio > 6, it can be reasonably postulated that the strength of the hollow pier will be unaffected by local compression flange buckling when the wall widthtothickness ratio is < 24, and it is entirely unnecessary to include diaphragms in hollow piers for stability. Additionally, it is equally interesting that the critical widthtothickness ratio of a hollow pier with a slenderness ratio > 4 derived using the proposed model is the same as the value given by the current AASHTOLRFD Bridge Design Specifications. x


Buitrago, Manuel; Adam, Jose M.; CalderÃ³n, Pedro A.; Moragues, Juan J.; Alvarado, Yezid A.  Estimating loads on shores during the construction of RC building structures  Structural Concrete  3/2016  502512  Technical Papers 
KurzfassungWhen constructing reinforced concrete (RC) building structures, knowing the loads to which the shoring system will be subjected during the entire process is one of the key aspects for ensuring safety during the work. Although various simplified methods of estimating the load transmission between shores and slabs during construction have been proposed to date, none of these methods can estimate the loads on individual shores during the different construction phases. This paper proposes a calculation method that allows the loads on individual shores to be calculated for each construction phase without having to resort to the use of advanced software. The proposal was validated by comparison with the results obtained from two actual buildings under construction and represents a step forward in the construction of RC building structures, as it is the first method that offers the possibility of estimating the loads acting on each shore during all the construction phases. x


fibnews: Structural Concrete 3/2016  Structural Concrete  3/2016  513519  fibnews  
KurzfassungTechnical Council meets in Madrid x
