It is known that the vast majority of buildings in Turkey are made out of reinforced concrete (RC). The 1999 Kocaeli and Düzce, the 2010 Elazig, and the 2011 Van earthquakes that occurred in Turkey ...revealed that the most significant factor in causing damage to buildings, or their collapse, was the use of low quality concretes, i.e., concretes with low strength values, in their construction This reveals that the load bearing members of these structures should be reinforced against the effects of possible earthquakes. The aim of the present study is to investigate the effect of carbon fiber reinforced polymer (CFRP) usage on the behavior of beams made out of low strength concrete. Within the scope of the study, the results of the experimental and numerical analysis for 14 RC beams, to which CFRP plates were applied on their lower surface, as well as for two reference beams, were presented for the case of collapsing. From the start of the test to the end, load, deflection and deformation data obtained from the beams were collected and then, by the identification of the collapsing mechanism as well as the load-deflection relation, the behavior of the beams was discussed in detail. In the numerical study, moment capacities were obtained for CFRP applied beams with different concrete strength values by using the material properties of the specimens examined in the mechanical test. The results of the numerical analysis were compared with those of the experimental tests, which were found to be consistent with each other.
The two-phase steels manufactured by means of cold die forging under the conditions of JSC “BelZAN” have good strength and ductility. At the same time, the use of the cold deformation method makes it ...possible to obtain parts of complex shapes. In the process of their production, production costs were reduced, as well as the influence of side factors on which the quality of the final product depends.
This paper aims to provide the reader a simple graphical method for the estimation of the concrete strength class (CSC) in existing reinforced concrete structures, which may be adopted even using ...limited concrete core drillings (less than three per test region) when compared to actual practice (European standards). The method is based on a combined probabilistic/empirical model for material properties of in situ concrete compressive strength and age-hardening effects. Assumptions are according to Eurocodes. The procedure has been subjected to a rigorous validation process. The principle of this approach is to use two graphs to mimic the role that in situ compressive strength test results play in determining the CSC of existing structures at the ages of the core drilling and of the construction time (28 days). Basis for the method are few considerations on: (a) age of concrete; (b) exposure environment; and (c) type of cement. Information from the two graphs is combined allowing valid and reliable estimates to be drawn. The proposed method is intended to be used as a clear alternative to classic methodologies and will be useful for professionals working in the field of structural rehabilitation. It reduces invasiveness, time expenditure and labour cost while maintaining high accuracy in estimations. Furthermore, it provides extra information about the concrete strength development that may be used to explore alternative scenarios in safety analyses.
The main requirements and criteria are provided in the article for selecting steels for cold bulk stamping of fasteners in the automobile industry: stamping capacity, component dimensions and ...configuration, the possibility of achieving the required component mechanical properties by heat treatment and strain hardening, and also the cost of starting workpiece and product manufacturing.
The influence of deformation and heat treatment on the mechanical properties of rebar steel is investigated on a pilot system. Specifically, with intermittent quenching and subsequent self-tempering, ...the intense-cooling time determines the tempering temperature of the quenched steel and hence the final mechanical properties of the rebar. The influence of the water pressure in the intense-cooling chamber on the uniformity of the mechanical properties is studied for steel with 0.31, 0.32, and 0.35% C; the water pressure is varied from 0.2 to 0.6 MPa. On that basis, it is established that the water pressure in the cooling chamber must be no less than 0.3 MPa, and the carbon content in the steel must be more than 0.32% in order to ensure that the mechanical properties of the rebar steel conform to the AT500 strength class according to State Standard GOST 10884–2004.
Structural timber is specific, because its quality is set by visual or mechanical grading. Visual grading method by PILODYN 6J device is examined in the paper. Experiments were carried out using 5 ...spruce boards (Picea abies Karst. L) from Slovakia. Dimensions of boards were 40 x 200 x 2500 mm. Density of wood was set by gravimetric method according to EN 408 (2013). Depth of penetrations was measured using the device PILODYN 6J (hp). Wood structure was described by the rate of growth (RoG) according to DIN 1052 (2004). Three most used visual grading strength classes C30, C24 and C18 according to EN 338 (2016) were specified. Dependencies between measured characteristics were expressed by multistage parallel scale model (penetration depth ~ number of growth rings ~ rate of growth ~ strength class and wood density). It is possible to predict visual strength class of board and indicative density of wood (EN 338) by the proposed model in situ. Methods of model are easy to use, reliable and economically undemanding.
Der Nachweis der Konformität ultrahochfester Betone (UHFB), die künftig in der im Entwurf befindlichen DAfStb‐Richtlinie „Ultrahochfester Beton“ geregelt sein werden, erfordert Formfaktoren, die eine ...Umrechnung zwischen den an UHFB‐Probekörpern unterschiedlicher Form und Größe erhaltenen Druckfestigkeiten erlauben. Bisher fehlten belastbare Versuchsergebnisse, auf deren Grundlage die Festlegung allgemeingültiger Formfaktoren zielsicher hätte erfolgen können. Daher wurde im Rahmen eines vom Deutschen Ausschuss für Stahlbeton geförderten Forschungsvorhabens der Einfluss der Probekörpergeometrie auf die Ergebnisse von Druckfestigkeitsprüfungen an normal‐, hoch‐ und ultrahochfesten Betonen experimentell untersucht. Die mittleren Zylinderdruckfestigkeiten der einzelnen Serien betrugen zwischen ca. 30 N/mm2 und 200 N/mm2. Mit Größtkorndurchmessern von 0,5 mm, 3 mm, 5 mm und 8 mm deckten die UHFB‐Systeme den Anwendungsbereich der zukünftigen DAfStb‐Richtlinie weitgehend ab. Neben Zylindern mit h/d mm = 300/150 und Würfeln mit einer Kantenlänge d = 150 mm, anhand deren charakteristischer Druckfestigkeit die Klassifizierung von UHFB erfolgen soll, wurden auch Zylinder mit h/d mm = 200/100 und Würfel mit einer Kantenlänge d = 100 mm untersucht. Die im Entwurf der DAfStb‐Richtlinie „Ultrahochfester Beton“ vorgenommene Klassifizierung von UHFB in die Festigkeitsklassen C130/140, C150/155 und C175/180 spiegelt den in den Versuchen beobachteten geringen Unterschied zwischen Zylinder‐ und Würfeldruckfestigkeit angemessen wider.
Effect of Specimen Geometry on the Compressive Strength of Ultra‐High Performance Concrete
The conformity check for ultra‐high performance concrete (UHPC), which is subject of the current draft of the DAfStb Guideline “Ultra‐High Performance Concrete”, requires factors that allow a conversion between compressive strengths obtained for UHPC specimens with different shape and size. Up to now, there was a lack of reliable test results that could form the basis for defining generally applicable conversion factors. Therefore, the influence of the specimen geometry on the results of compressive strength tests on normal strength concrete, high strength concrete, and UHPC was investigated experimentally within the scope of a research project funded by the German Committee for Structural Concrete. The mean cylinder compressive strengths of the individual series ranged between approx. 30 MPa and 200 MPa. With maximum grain sizes of 0.5 mm, 3 mm, 5 mm, and 8 mm, the UHPC mixtures largely covered the scope of the forthcoming DAfStb Guideline. Besides cylinders with h/d mm = 300/150 and cubes with an edge length d = 150 mm, whose characteristic compressive strength will be used to classify UHPC, smaller cylinders with h/d mm = 200/100 and smaller cubes with d = 100 mm were tested. The draft of the DAfStb Guideline “Ultra‐High Performance Concrete” classifies UHPC by the strength classes C130/140, C150/155 and C175/180. The denominations adequately reflect the small difference between cylinder and cube strength observed in the tests.
ABSTRACT
Although cross‐laminated timber (CLT) plates are increasingly used in high‐performance building structures, a tailored composition of them or, at least, a performance‐based classification ...scheme is not available. Especially, the influence of the quality of the ‘raw’ material (wooden boards) on the load carrying capacity of CLT elements is hardly investigated yet. For this reason, within this work, bending tests on 24 CLT plates consisting of wooden boards from three different strength classes have been carried out. The global mechanical response as well as the formation of failure mechanisms were investigated, including a full‐field deformation measurement system, which allowed for a qualitatively as well as quantitatively identification of board failure modes. Interestingly, no influence of the board strength class on the elastic limit load of the CLT plates was observed, but the situation was different for the load displacement history beyond the elastic regime, where basically, two different global failure mechanisms could be distinguished. The obtained knowledge about the ‘post‐elastic’ behaviour of CLT plates may serve as a basis for the optimisation of CLT products and the development or improvement of design concepts, respectively. Moreover, the obtained large ‘post‐elastic’ capacity reserve of CLT consisting of high quality boards could lead to a better utilisation of the raw material.
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