محسن احمد حسن حبل المتين

Due to the importance of using ambient friendly available materials as an alternative solution instead of the tradition materials in the field of civil construction, present study focuses upon this solution to explore its ability and efficiency when using in the structural members. One of such modern materials is the geopolymer or alkaline concrete which is considered as a green concrete that reduces the evolution of the dioxide carbon during the production process. Also, the recycled components represented by the crushed rubble concrete as course and fine aggregate are also considered here to increase the dependence on the ambient friendly materials that consist the produced geopolymer (green) concrete. In the present study, the geopolymer concrete mix, alkaline concrete with recycled aggregate, is used within the compressive structural elements represented by short hollow steel columns having equal square sections. These columns are tested with and without grouted green concrete as a strengthening material. Usually, the alkaline concrete is produced based on certain molecular ratios that governs the strength of the concrete mix in addition to the role of aggregate ratio. Hence, two values of molecular ratios are adopted in this paper as variable parameters in the concrete mix. Both of the geopolymer concrete mixes are compared with the normal concrete mix as strengthening materials grouted inside the hollow steel columns. Results of axially loaded specimens show that the use of geopolymer (alkaline) concrete with recycled aggregate and different molecular ratios enhances the strength of the steel columns under compressive loads.

This paper investigates the change in the natural frequency of whole building due to the increase or decrease of the number of floors of a steel building model. Five steel building models were adopted in the present study to investigate the natural frequency required to be identified in each model. The first model represents a one floor building model, the second building model contains two floors and so on. The first four models were subjected to further masses distributed upon four points within the last floor. Each model consists of the same structural details that are proposed in the other models such as details of the beams, columns and slabs. The herein parameters are the number of floors and the further added masses upon the models up to four floors. All models were analyzed using ANSYS software to identify the natural frequencies for the extracted modes of vibration about X, Y, and Z building axes. The study is aimed to produce a relationship between the change of floors number and the further mass addition in the field of structural frequency attenuation based on the indication of the first identified mode. Results show that higher masses required to be added to attenuate value of natural frequency for the one floor building model than the further masses required for building with two floors to achieve the same purpose. This relationship continues for the other models with higher number of floors but with less further required masses.

Geopolymer or alkaline concrete is a modern binder material characterized as an ambient friendly product within the construction field. Present study has investigated the geopolymer concrete mix used in the dome structural members compared with the use of ordinary concrete mix. Geopolymer concrete mixes are produced according to certain molecular ratios govern its design strength, so that present study has adopted molecular ratio of 14 mole (14M) as an alkaline molar concentration forming a binder material for the coarse and fine aggregate. Laboratory tested coarse and fine aggregate were used in both of geopolymer and ordinary concrete mixes. Two models of domes were made using geopolymer concrete mix while other two models were casted by the ordinary concrete mix and both types were reinforced with single layer of steel wire mesh. Later, all models were tested under uniaxial concentrated load …

Steel sections are usually manufactured with geometric defects and deviates from the original ideal shape during rolling process; these defects are called imperfection in international standards. This study is devoted towards investigating local geometric imperfections of steel columns under combined effect of axial load and lateral cyclic displacements which simulates steel columns under seismic events. Ten wide flange sections with two cases for each section: ideal and imperfect. A comprehensive nonlinear finite element model which is validated against available experimental data in literature was employed. A sustained axial load which ranges from 20-100 percent of the maximum axial capacity for the column was applied prior to application of the designated lateral cyclic displacement amplitude. It was found that web local imperfection has a substantial impact on the cyclic response of the columns. It was also revealed that higher axial load ratios impact column response than do lower load ratios. Moreover, drift angle was found more susceptible in stocky than in light sections. The study showed that there is a limiting zone within the slenderness ratios for both of flanges and web should be avoided when considering section design of columns under seismic events because it yields a big difference between ideal and imperfect section.

Several techniques were considered to retrofit the reinforced concrete members suffering damages or design mistakes. The present study investigates experimentally using a tightened bar system as an externally applied reinforcement installed straightly to provide additional strength to the partially or completely damaged concrete beams. The study involves testing 13 reinforced concrete beams classified into two groups based on the location of the externally applied reinforcement, either one bar installed beneath the lower face of the beam or two bars added to both sides of the beam. The study also investigates changing the loading ratio during the first stage of loading (40, 80, and 100) % of the ultimate load capacity of the control specimen. The third adopted parameter was the location of anchorage system devices for the beam edges, which was 10 cm or 25 cm. The results exhibited that the externally straight threaded tighten steel bar enhanced the ability of partially or completely damaged concrete beams to withstand additional loading in the range of (4–69) % above the original ultimate load capacity of the beam. Furthermore, the anchorage system on the bottom side of the beam was more efficient than the anchorage system on both sides. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2024.

This paper investigates the impact of explicit initial geometric imperfections on the seismic response of wide flange steel column sections in moment resisting frames. Ten wide-flange sections (five light and five stocky) were chosen in the parametric investigation. The columns were subjected to a combined effect of axial load and lateral cyclic displacement protocol as per ASCE guidelines. Target axial load ranging from 20 to 100 of the column axial capacity was chosen to cover a wide range of axial loads employed in practice. Nonlinear finite element was used to conduct the analyses throughout the paper. The theoretical models were validated against available experimental data. The study indicated that the reduction in the drift angle capacity of the imperfect compared to the straight sections is approximately ranging between 0% and 60% for various axial load ratios. Results has also revealed that the effect of imperfection is more pronounced for stocky steel sections under high axial load ratios, although other sections responded in a variable degrees. Design recommendations were proposed to aid in better simulation of advanced structural analyses. © 2023, Korean Society of Steel Construction.