Jiří Maca

The response of grandstands driven by filtered Gaussian white noise processes

Abstract This paper presents a semi-analytical estimate of the response of a grandstand occupied by an active crowd and by a passive crowd. Filtered Gaussian white noise processes are used to approximate the loading terms representing an active crowd. Lumped biodynamic models with a single degree of freedom are included to reflect passive spectators occupying the structure. The response is described in terms of the first two moments, employing the Ito formula and the state augmentation method for the stationary time domain solution. The quality of the approximation is compared on the basis of three examples of varying complexity using Monte Carlo simulation based on a synthetic generator available in the literature. For comparative purposes, there is also a brief review of frequency domain estimates.

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.

Human-Induced Loads on Grandstands as Non-Stationary Gaussian Processes

In this contribution, we employ non-stationary filtered Gaussian processes as an enrichment of a periodic mean value in order to approximate crowd loads on grandstands. Our work generalizes previous considerations where the superposition of a mean value and a stationary filtered Gaussian noise was used, and helps therefore to better predict the response of a structure mainly in the transition stages. We specify general theory of stochastic differential equations within the context of grandstands by recalling particular moment equations, and demonstrate its benefits or drawbacks on two simple examples. Overall performance is measured in terms of the second moment evolutions in time and in terms of the total up-crossings of the systems response compared to previously developed stationary approximation and Monte Carlo simulation. Throughout, only an active part of a crowd is considered.

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.

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.

COMPARISON OF METHODS USED FOR SEISMIC ANALYSIS OF STRUCTURES

This paper investigates effects of the seismic load to a structure. The article describes main methods of the definition and practical application of the seismic load based on the Standard Eurocode 8. There was made a comparison of all methods using the same structure. A simple two-storeyed concrete 2D-frame with fixed joints was chosen. A one another model with rigid beams for some calculations was defined. The second model can be used for hand-calculations as a cantilever with two masses. The paper describes main dynamic properties of the chosen structure. Seismic load was defined by lateral force method, modal response spectrum, non-linear time-history analysis and pushover analysis. The time-history analysis is represented by accelerograms. There were made linear and non-linear calculations.

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.

Seismic Assessment of Unreinforced Masonry Buildings

The first case study used in this work is an existing seven-storey unreinforced masonry building (representing a typical residential building located in the district of L ́Example in Barcelona). The accuracy of the non-linear static procedures was evaluated by comparison with non-linear dynamic analyses for seven ground motion records and different levels of seismic intensity. The results obtained from the analyses showed good performance of the static pushover methods on the analysed building. The second case study used in this work is a two-storey unreinforced masonry building which was tested at ELSA in Ispra, Italy. First a modal response spectrum analysis was carried out. Subsequently, non-linear static analysis was performed using two different computer programmes. The results of the present work were compared with experimental results.

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.

The Efficiency of Dynamic Relaxation Methods in Static Analysis of Cable-Membrane Structures

This paper is focused on the static analysis of cable-membrane structures using the dynamic relaxation method. Several different processes of dynamic relaxation method are compared in this paper. The techniques with viscous damping and the techniques with kinetic damping are used. The efficiency and stability of each process are compared to selected 3D examples of cable-membrane structures. The effect of mass distribution along the structure is also of interest and it is studied in the paper.