Karlis Rocens

Decreasing displacements of prestressed suspension bridge

Abstract A suspension bridge is the most suitable type for a long-span bridge due to rational use of structural materials. Increased deformability, which is conditioned by the appearance of the elastic and kinematic displacements, is the major disadvantage of suspension bridges. The problem of increased kinematic displacements under the action of symmetrical and non-symmetrical load can be solved by the prestressing. A prestressed suspension bridge with span of 200 m was considered as an object of investigations. The cable truss with the cross web was considered as the main load carrying structure of prestressed suspension bridges and was compared with the single cable. The considered prestressed suspension bridge was investigated by the FEM program ANSYS 12 and by the small scale physical model. Rational, from the point of view of minimal vertical kinematic displacements, main load-carrying structure of prestressed suspension bridge was developed. The obtained results shows, that usage of cable truss wit...

Utilization of Composite Materials in Saddle-Shaped Cable Roofs

A saddle-shaped cable roof formed by two orthogonal groups of cables joined with a compliant support contour is considered. The kinematic invariability of the roof obtained by prestabilizing the cables makes it possible to avoid heavy slabs of reinforced concrete in the construction of roofs and to use light composite materials. The main geometric characteristics for a cable roof with CFRP load-carrying and contour cables and steel stabilizing cables are determined by a numerical experiment.

The effect of material strength on the behaviour of concrete‐filled steel elements

Abstract Composite columns and beams are a combination of concrete and steel elements realising the advantages of both types of materials. According to codes for concrete‐filled column, the plastic resistance of the cross‐section is given as a sum of the components and taking into account the effect of confinement in case of circular sections. In this study the stress state in composite column is determined taking into account non‐linear relationship of the modulus of elasticity and Poissons ratio on the stress level in the concrete core. It has been determined that the effect of confinement occurs at a high stress level when structural steel acts in tension and concrete works in lateral compression. The stress state and load bearing capacity of section in bending is determined taking into account non‐linear dependence on position of neutral axis. Because the ultimate limit state of material is not attained for all the parts simultaneously, to improve the stress state of a composite element and to preven...

Prestress Losses in the Stabilizing Cables of a Composite Saddle-Shaped Cable Roof

The paper deals with a square composite saddle-shaped cable roof 30 × 30 m in the plan, which is formed by two orthogonal cable groups joined with a compliant support contour. The kinematic invariability of the roof is achieved by prestressing the cable net. From the viewpoint of material consumption, the cable roof has rational geometrical characteristics. A hybrid composite cable on the basis of CFRP, GFRP, and steel is considered as a material for contour cables. The load-carrying and the stabilizing cables are made of steel. Prestress losses in the stabilizing cables are determined for three variants of prestressing. The possibility of reducing the consumption of cable materials by prestressing each cable of the net by an individual force is revealed.

Prestressed Cladding Elements for Tensioned Structures

Two types of prestressed cladding elements for the long span cable roofs were investigated. The first considered type of prestressed cladding element was pneumatic and formed by the generally woven by the basket weave fabric from the Vectra (LCP) yarns, which is covered by the PoliTetraFluoroEthylene (PTFE) copolymer foil, and compliant contour, consisting from the several glued together layers of the mentioned covered fabric. The second considered type of prestressed cladding element was formed by the steel cables steel pipes and the same type of covered fabric as the first type. Rational from the point of view of materials consumption heights and levels of prestressing for two considered types of cladding elements were evaluated.

Experimental Determination of Natural Frequencies of Prestressed Suspension Bridge Model

Abstract A suspension bridge is the most suitable type for a long-span bridge. Increased kinematic displacements are the major disadvantages of suspension bridges. This problem can be solved by application of prestressed cable truss. Dynamic approach is one of regulated bridge design parts. Determination of natural frequencies of a physical model of a prestressed suspension bridge is presented in this paper. Natural frequencies, as mode shapes, of the model depending on a prestressing level were determined. It was shown that a mode shape with one half wave did not appear. Experiments showed that dynamic characteristics of prestressed suspension bridge could be regulated by changing a prestressing level, which excludeda possibility of resonance appearance.

Curvature analysis for asymmetrical multi-layer composite

Curvature analysis for asymmetrical multi-layer composite One possibility to reduce material consumption in bent construction is flat plate replacement with curved or saddle shaped plate (shell). This solution is beneficial in case of plywood sheet, provided that curved or saddle shaped plates are made in widely used multilevel plywood presses with parallel shelves. Curvature is gained by using layers with required physical properties, geometric dimensions, orientation, creating structurally asymmetrical material, relative to mid-surface. While it is conditioning in different moisture-temperature conditions, it gains projected shape.

Glued Joint Behavior of Ribs for Wood-Based Composite Plates

This article presents experimental investigations of composite sandwich plywood plates with cell type core and their connections between skin layers of birch plywood and a core of straight and curved plywood honeycomb-type ribs. This shape of core ribs provides several improvements for these plates in the manufacturing process as well as improves the mechanical properties of plywood plates. This specific form of ribs allows simplifying the manufacturing of these plates although it should be detailed and improved. The most typical cases (series of specimens) were compared to the results obtained from FEM (ANSYS) simulations. All thicknesses of elements are chosen according to plywood supplier assortment. Standard birch plywood (Riga Ply) plates were used - three layer plywood was chosen for skin elements (Surfaces) and three or five layer plywood was chosen for edge elements. Different bond pressures were taken to compare their influence on joint strength and stiffness.

Prestressed Cladding Element for Cable Roof

Prestressed cladding element for cable roof Prestressed cladding element for the long span saddle-shaped cable roofs was considered. Peculiarity of the cladding element is absence of rigid contour. The load bearing cables of the roof supports prestressed cladding element. The generally woven by the basket weave fabric from the Vectra (LCP) yarns, which is covered by the PoliTetraFluoroEthylene (PTFE) copolymer foil, steel cables and steel pipes were considered as the materials of covered fabric, load-bearing cables and central pillar, correspondingly. The covered fabric is joined directly with the cables of saddle-shaped roof and the displacements of the cables have significant influence on the prestressing level of cladding element. Influence of the displacements of 50×50 m cable net of saddle-shaped roof on the prestressing level of cladding element was evaluated. The design loads combination includes dead weight, accidental snow load and prestressing. It was shown, that the maximum vertical displacements of prestressed cladding element changes within the limits from 34.80 to 43.27 mm, when the level of prestressing for tensioned fabric and heights of prestressed cladding element changes within the limits from 0.2 to 0.6 from it load bearing capacity and from 0.25 to 1.00 m, correspondingly.