Hastia Asadi - Academia.edu (original) (raw)

Papers by Hastia Asadi

The negative impact of water must be considered during the design of architectural coated woven f... more The negative impact of water must be considered during the design of architectural coated woven fabrics which are sensitive to water attacks. It is known that the uniaxial tensile strength of glass-PTFE materials does degrade with water attack. This contribution quantifies the possible tensile strength reduction of different types of glass-PTFE materials under various water exposure conditions. This includes not only water exposure of unsealed cutting edges, as they, e. g., exist in weld seams, but also water exposure of the glass fibres through the PTFE coating. Experimental results show that both water exposure methods lead to similar degradation effects. From the acquired values of degradation, strength modification factors have been derived using the principles of the new European Technical Specification prCEN/TS 19102 "Design of tensioned membrane structures".

Structural Engineering and Mechanics, 2018

Numerical Methods in Civil Engineering, 2017

The theory of optimization has improved remarkably during the last four decades. The main part of... more The theory of optimization has improved remarkably during the last four decades. The main part of optimizing investigations has been focused on enhancing buckling resistance which does not violate the economic feasibility of final design. The finite element analysis which is called ESO (Evolutionary Structural Optimization) is presented for optimum (or most ideal) design of columns to increase the buckling resistance of structures. To attain the significant design variables, this method can be employed to choose an appropriate, affective and economical way. During an iterative process, the above approach ensures the attainment of global maximum critical load under the imposed equality volume constraint, type of boundary conditions and type of cross sections. Precise results and numerical examples have been shown and useful diagrams have been developed for the cases of simple, clamped and clamped free supported by different types of cross-sectional areas. The model has succeeded in arriving at the global optimal column designs possessing the absolute maximum buckling load without violating the economic feasibility requirement. As a matter of fact, the cross sectional area of column changes whereas, the total volume of column remains constant. As a result, the buckling forces increase. According to this study critical buckling load of columns decreases by changing the boundary condition from clamped to clamped free and then simply supported.

10th edition of the conference on Textile Composites and Inflatable Structures, 2021

IABSE Symposium, Prague 2022: Challenges for Existing and Oncoming Structures

The design process of tension fabric structures must consider changes of the material properties ... more The design process of tension fabric structures must consider changes of the material properties due to long-term exposure to the environment. In line with the harmonized view of the Ultimate Limit State verification which is currently developed in the framework of a novel European design standard for membrane structures, a strength modification factor considering ageing effects is proposed to describe the deterioration arising from environmental impacts. The objective of this paper is to broaden the data basis for the long-term behaviour of a typical structural membrane made of PET-PVC material for environmental impacts. In this way, an overview about different data achieved from two practical applications and experimental artificial weathering tests is presented for the destructive effect of weathering on tensile strength of coated woven fabrics. Finally, related weathering-induced ageing modification factors are derived.

The design process of membrane buildings and structural fabrics has to consider changes of the ma... more The design process of membrane buildings and structural fabrics has to consider changes of the material properties due to long-term exposure to the environment. For the structural engineer the loss of tensile strength in the fabric, in the seams and in the mechanical fastenings is of major concern, further variations in tear strength and stiffness should be known. The degradation of the protective coating normally becomes apparent in the decrease of the optical properties, first. For basic synthetic materials the strength deterioration resulting from certain environmental impacts are known. But the prediction of properties for material compositions typically found in structural membranes are vague and a change of these properties during lifetime due to a time dependent environmental load spectrum containing UV radiation, condensate, rain, temperature and pollutants is not possible without experimental testing. Regarding long-term loading behaviour of structural membranes, creep-rupture or time-tofailure-tests are state of the art. A reevaluation of existing literature and new experimental results show that these tests do not cover loads with limited duration like snow. The objective of the present paper is to broaden the data basis for long-term behaviour of typical structural membranes for both environmental impacts and mechanical loading. Both aspects are investigated in contribution to the development of a new European design standard for structural membranes. PVC-coated polyester (PES) fabrics and PTFE-coated glass fiber fabrics are in the main focus of the standardization work as they cover the gross market for structural fabrics. In this paper, environmental impacts to the top coat, particular due to humidity are discussed for PES/PVC and glass/PTFE fabrics. Furthermore, effects of "long-term loading" but with limited duration are presented for glass/PTFE fabrics. Moreover, consequences on the linked strength reduction factors derived from the test results are analyzed and the implications on the design concept and test methods are discussed.

Construction and Building Materials

Advances in Structural Engineering, 2018

Architectural fabrics consist of woven base cloth protected by a coating on both sides. Corrosive... more Architectural fabrics consist of woven base cloth protected by a coating on both sides. Corrosive liquids or vapours may diffuse through the matrix material and corrosion effects on fibres may lead to substantial reduction in mechanical properties. Tensile strength is of most importance for the safety of a structure and strain properties govern its serviceability. Wetting is one of the main environmental impacts. Due to rain, condensation or snow melting cycles, the membrane gets wet. If the fabric under the coating gets wet and to which amount depends on the condition of the covering coating over the lifetime of the architectural structure and on the wicking properties of the fabric material. Water penetration influences the fabric’s properties. How and to what extent is the field of investigations of this article. The influence of water on the tensile strength and the breaking strain of two common architectural fabrics, polyester (PES)/ polyvinylchloride (PVC) and glass/polytetrafluoroethylene (PTFE), are investigated. Virgin and aged materials are examined.

One of the most important mechanical properties of architectural fabrics is the tensile strength,... more One of the most important mechanical properties of architectural fabrics is the tensile strength, which is measured by uniaxial tensile tests. Considering gripped width of the specimens, there are two principal kinds of uniaxial tensile strength tests: strip and grab tests. In the strip test, the test specimen is clamped over the whole width whereas in the grab test only the middle part of the width is clamped. Both are included in test standards for uncoated and coated fabrics. These test standards are also applied in the context of textile architecture. Until now, only few studies have focused on them. The users and constructional partners are left alone to decide which test method fits better for structural applications. Frequently it is assumed that the choice depends on the specific architectural textile to be tested, e. g. woven or knitted fabric, coated or uncoated, rather stiff or rather flexible coating etc. In one standard, the grab test is recommended as an alternative wh...

Materials, 2021

Polytetrafluoroethylene (PTFE)-coated glass fiber fabrics are used for long-lasting membrane stru... more Polytetrafluoroethylene (PTFE)-coated glass fiber fabrics are used for long-lasting membrane structures due to their outstanding mechanical properties, chemical stabilities, and satisfying service life. During their operation time, different environmental impacts might influence their performance, especially regarding the mechanical properties. In this contribution, the impact of water on the tensile strength deterioration was assessed experimentally, providing evidence of considerable but partially reversible loss of strength by up to 20% among the various types of investigated industrially established fabrics.

Materials

In the past five decades, reinforced coated textile membranes have been used increasingly as buil... more In the past five decades, reinforced coated textile membranes have been used increasingly as building materials, which are environmentally exposed. Thus, their weathering degradation over the service life must be taken into account in design, fabrication, and construction. Regarding such structural membranes, PVC (polyvinylchloride)-coated PET (polyethylene terephthalate) fabric is one of the most common commercially available types. This paper focuses on the backbone of it, i.e., the woven PET fabric. Herein, weathering of uncoated PET, as the load-bearing component of the composite PET-PVC, was studied. This study assessed the uniaxial tensile strength degradation mechanisms of uncoated PET fabric during artificial accelerated weathering tests. For this purpose, exploratory data analysis was carried out to analyze the chemical and physical changes which were traced by Fourier transform infrared spectroscopy and molecular weight measurements. Finally, with the help of degradation m...