Miroslav Bajer

Strengthening under Load: Experimental and Numerical Research

The paper presents experimental and numerical research of strengthening of columns under load using welded plates. Three sets of three columns each were tested. All columns were 3 m long. The load from loading cylinders was transmitted through knife-edge bearings, which ensured pinned boundary condition perpendicular to the weaker axis. Set (A) comprised columns with welded T shaped cross-section. Set (B) comprised columns with welded monosymmetric I shaped cross-section. Both sets (A) and (B) had been loaded monotonically until collapse occurred. Set (C) contained columns with T shaped cross-section with the same dimensions as the columns in set (A). The columns from set (C) were first loaded to 70 kN. The force was being held constant and the second flange was being welded to the web under load. After the welding process was finished and the specimen cooled, the column was loaded to failure. The average forces at collapse of column sets (A), (B) and (C) were 143 kN, 308 kN and 323 kN, respectively. It was unexpected that the columns strengthened under load (C) had higher average resistance than the columns welded without preload (B). It could be caused by the residual stress and distortion caused by welding. The study includes the results of finite element models of the problem created in ANSYS software. The results from the experiments and numerical simulations were compared.

Strengthening of Steel Columns under Load: Torsional-Flexural Buckling

The paper presents experimental and numerical research into the strengthening of steel columns under load using welded plates. So far, the experimental research in this field has been limited mostly to flexural buckling of columns and the preload had low effect on the column load resistance. This paper focuses on the local buckling and torsional-flexural buckling of columns. Three sets of three columns each were tested. Two sets corresponding to the base section (D) and strengthened section (E) were tested without preloading and were used for comparison. Columns from set (F) were first preloaded to the load corresponding to the half of the load resistance of the base section (D). Then the columns were strengthened and after they cooled, they were loaded to failure. The columns strengthened under load (F) had similar average resistance as the columns welded without preloading (E), meaning the preload affects even members susceptible to local buckling and torsional-flexural buckling only slightly. This is the same behaviour as of the tested columns from previous research into flexural buckling. The study includes results gained from finite element models of the problem created in ANSYS software. The results obtained from the experiments and numerical simulations were compared.

Composite Slabs with Prepressed Embossments – Longitudinal Shear Resistance

Composite slabs with prepressed embossments present an effective solution for horizontal structures. Prepressed embossments ensure composite action after hardening of concrete. Longitudinal shear failure mode typically governs if the shear resistance of embossments is not sufficient for full composite action. Mutual separation of thin-walled sheeting from concrete and its deformation inside the rib is characteristic for this failure mode. Design methods for composite slabs use full scale bending tests in several series to determine their bearing capacity. A less expensive alternative is to use small-scale shear tests to determine shear characteristics of the sheeting. This paper presents detailed numerical models of slab in shear and models of slab in bending with and without embossments. These models are compared with previously performed experiments. Key WordsComposite slab; steel sheeting; concrete; prepressed embossment; longitudinal shear; experiment; numerical model

Shear Tests of Composite Slabs, Experimental and Numerical Investigation

Composite slab is being used for horizontal structures. The sheeting can serve as a permanent formwork and no additional reinforcement can be required. The slabs are then fast and easy assemble construction which can be effectively used in reconstructions. One of the meanings to assure composite action of composite steel-concrete slabs is prepressed embossments. Its main disadvantage is that the design of a new type of sheeting requires expensive and time consuming large-scale laboratory testing which hamper its widespread commercial usage. Small-scale shear tests present a less expensive alternative to the large-scale tests but its results cannot be simply used for the design of the whole slab. The results from small-scale tests with different options are compared in this paper. Also a possibility of contribution of FE simulation results to the small-scale tests usage is investigated.

Bonded Anchors In High Performance Concrete

The design of chemical anchor elements presents an ever-topical challenge. Bonded anchors have been in use for many years, but their main field of application is still in concrete with common strength characteristics. This paper summarises the results of experimental and numerical research focused on determination of the behaviour and bond strength limits of what are currently the most widespread industrial glues used for anchor bonding. The goal of this research is to find the limits of the effective use of such glue types in high performance concrete, and also to verify the most commonly used design methods for bonded anchors. The progress and configuration of the experiments are described.

Experimental Analysis Of CompositeSteel-concrete Slabs

Composite structures fabricated from thin-walled steel sheeting and concrete slabs are especially suitable for roof and floor bearing structures. Using embossments for the shear connection between the sheeting and the concrete simplifies and accelerates the construction process because it ensures the composite action of the two materials without any need for additional reinforcement. This article is focused on this type of connection. It contains a short review of thin-walled sheeting manufactured in Western Europe and presents results obtained from the experimental testing of specimens. These specimens were tested by vacuum loading and by cyclic loading in four-point bending tests. Small scale specimen tests were performed to determine the shear behaviour and to adjust numerical models.

Experimental approach of the single pedestrian-induced excitation

Experimental approach of the single pedestrian-induced excitation Pedestrian-induced vibrations are a criterion for serviceability. This loading is significant for light-weight footbridge structures, but was established as a basic loading for the ceilings of various ordinary buildings. Wide variations of this action exist. To verify the different conclusions of various authors, vertical pressure measurements invoked during walking were performed. In the article the approaches of different design codes are also shown.