Petr Fajman

The efficiency of dynamic relaxation methods in static analysis of cable structures

Nine different schemes of dynamic relaxation method are compared in the paper. Schemes with viscous damping and schemes with kinetic damping are used. Kinetic damping with a peak in the middle of the time step and kinetic damping with the parabolic approximation of the peak are considered. They are also used in three different ways of cable approximation. The cable is approximated as a tension bar, a catenary and a parabolic cable element. The efficiency and stability of each method are compared to three selected 3D examples of cable structures and one existing structure. The effect of mass distribution along the structure is also of interest and is studied in the paper.

The Experimental Observation of the Prestress Forces in the Structural Elements of a Tension Fabric Structure

The periodic experimental observation of the prestress forces in some selected structural elements of the tension fabric structure is mentioned in this paper. The described experiment was focused to the tension fabric roof which covers the tram stop K Barrandovu in Prague. So far the observation was performed three times and it was every time aimed on three types of basic structural elements support cables anchored to the ground, edge cables placed in a fabric pocket and fabric membranes. The used non-destructive experimental procedures are based on the geometrical nonlinearity and the frequency method, the applied measurement system was developed by authors. The dependence of cable forces on temperature changes can be found out from the obtained results.

Utilization of Splice Skew Joint with Key on Reconstruction of Historical Trusses

Currently, for reconstruction of historical trusses traditional carpentry joints are used. For many years these joints are constructed in the same way. Unfortunately, the mechanical behaviour of these joints and influence of their parts and geometry of joints to the joint stiffness are not well known. To improve these joints, it is necessary to know their behaviour. This paper describes a study recently completed on the vertical splice skew joint with a key. Experimental tests were performed and compared to the numerical results of three-dimensional finite element model created using ATENA 3D.

The effect of inclination of scarf joints with four pins

ABSTRACT During the renovation of roof trusses and roof structures, damaged wood must be replaced with new wood. To keep the original material adjustment slab joints can be used. Unfortunately, this type of joint has not been observed from the structural perspective. The shape of the joint, the inclination of its faces, the type and the number of connectors still represent an unknown area. A simplified analytical model is briefly derived in the article and the effect of the face inclination is solved. The results obtained from experiments are compared with the results from the model.

Cable-Membrane Structures - Numerical Analysis and Practical Application

This paper presents a practical application of form-finding process of cable-membrane structures. The dynamic relaxation method with kinetic damping is used as the computation method for numerical analysis. A brief description of the construction, a description of the models and the way of solving tasks will be introduced. The correct operation of the implemented algorithm will be compared with a commercial program.

Carrying Capacity Testing of Membrane Connection

This paper is focused on carrying capacity testing of five different types of membrane connections. Three reference samples for each type of connection were tested for tensile strength. Low measured peak force value and especially the way breakage outside of the join indicative of a wrong material, and not on the connection. The obtained values were compared with technical datasheet of the material manufacturer, which has been non-compliance. It confirms the assumption that the material was changed, which could harm to the user.

Bearing Capacity of a Scarf Joint

The bearing capacity of a scarf joint depends on the length of the joint and the type of connection. It is possible to use circular bolts or squared dowels. Both connection tools used in the repairs of historic timber structures are made of wood according to the requirements of the heritage authority.

Efficiency of Dynamic Relaxation Method in Form-Finding Process of Cable-Membrane Structures

This study is focused on the form-finding process of cable-membrane structures using the dynamic relaxation method with kinetic damping. Eight different schemas of the dynamic relaxation method are compared in the paper. The effect of mass distribution along the structure is also of interest. The efficiency and stability of each process are compared on selected 3D examples of cable-membrane structures.

Diagnostics of an Existing Cable-Stayed Bridge by Means of the Dynamic Load Test

The cable-stayed bridge at the inner ring road in Prague in the Czech Republic was put into operation in 1997. In 2008 a crack was found in the bridge structure area where the end beam was connected with the upper deck of the box section and where the bridge expansion joint system was anchored. The basic objective of diagnostic works, which were started immediately after the finding of the crack, was obtaining the basis for bridge structure modifications, among other things, to prevent formation of similar damages in the future. A series of diagnostic methods was used for determination of the bridge actual state and the real static and dynamic bridge behavior. One of these methods was the dynamic load test. It was focused on an examination of the bridge forced vibration which was caused by dynamic effects of a usual traffic flow. An arrangement of the test was not quite usual because the experiment was concentrated on dynamic behaviour of bridge support areas especially. The abutment area, the pylon area and the area of a pillar with the bearing with a tensile structural element were observed on the investigated bridge. The dynamic load test was performed in two stages. The first stage was focused on investigation of bridge dynamic behaviour in original structural conditions and on obtaining the basis for design of bridge adjustments. The second stage was realized after bridge reconstruction in December 2012 and verified the effectiveness of bridge modifications.

Historical Timber Structures with Selected Joints

Repairs of historical timber structures lead to connecting existing and new beams. The requirements for beam authenticity make use of older ways of connecting. The first type is the splice of beams in bending with the scarf joint, rafters and tie-beams are joined with the dovetail and, finally, the connection of the main joist with the strut is by the mortise carve.