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In the present study, the effect of the structural simplicity on the progressive collapse resistance of a 13-story RC framed building is assessed. The existing structure from Brăila (a zone with high seismic risk from Romania) designed in 1972 according to the former seismic code P13-70, was re-designed in accordance to the provisions of the current seismic code P100-1/2013. The original building consists of beams and columns with different cross-sections along the height of the structure. To achieve the objective of this study, a new model with constant cross-sections was designed according to the current seismic and structural concrete codes. Following the provisions of the GSA (2003) Guidelines, nonlinear dynamic analyses are performed using the Applied Element Method incorporated in the ELS® computer software. It was shown that, under the standard GSA loading (DL+0.25LL) the both two numerical models of the 13-story building are not expected to fail when a first-story corner column is suddenly removed. To estimate the ultimate load-bearing capacity of the structural models, a series of nineteen nonlinear dynamic analyses are carried out. The robustness analyses indicate that, the model with different cross-sections can sustain a maximum load 16% larger than the model with constant cross-sections along its height.

This paper investigates the structural response of RC framed buildings subjected to accidental/abnormal loads (explosion, impact and other hazards). Several existing national or international design codes (GSA 2003, DoD 2009, 2013) provide limited guidelines for the assessment of progressive collapse resistance in the design process and the alternate load path method is widely used in current structural design codes. Since the progressive collapse is a dynamic and nonlinear event the structural components undergo nonlinear deformations before failure. In this study the nonlinear procedures (NSA and NDA) are applied. These types of analyses imply significant computational power and time costs. In addition, the reinforced concrete framed structures are able to develop multiple post flexural resisting mechanisms. These are currently not considered in the structural analyses performed according to GSA2003 and DoD2009 provisions. Thus, the first objective of this paper is to identify by numerical computation the presence and contributions of such supplementary resisting mechanisms. A further objective is to determine what will be the influence on the accuracy of results when, starting from the original structure, the number of its bays is successively reduced; also, what is the efficiency in saving run-time costs when such simplified models are considered in the analysis. The study reveals that in order to resist abnormal loads, RC structures are able to develop supplementary resisting mechanisms beyond the flexural behavior and respectively, important time savings are obtained without significantly affecting the results accuracy.

In order to streamline the mixes of concrete with powder waste glass as small as < 0.250 mm, a postdoctoral program objective was to test the activity rate of its pozzoolanic reaction, through various methods and by comparing it with other powders reactions in a standardized cement composition. The first method was to determine the compressive strength of cement mortars, partially substituted by glass powder, silica fume, ash and clay. The second method was determining the chemical composition of the powder with fluorescence X-ray, XRF type. The third method, was based on fragments of mortar studied and subjected to microscopic observations – SEM determination (scanning electron microscopy) to investigate the microstructure of the raw material.

We live in an era where people should be more aware of pollution and its consequences. The present paper reveals a way protecting the environment while producing high quality concrete. What make this type of concrete environmentally friendly are the recycled aggregates in the concrete composition amongst with eliminating the ecological impact by saving large amounts of natural aggregates resources. Recycling concrete comes with many other advantages that lead to waste reduction, economy in waste transportation and storage taxes, which are becoming increasingly expensive. This research is based on mix design and experimental tests carried out on C20/25 strength class concrete with uncontaminated leftover concrete aggregates (LCAgg). It reveals favorable results in order to militate for recycled concrete aggregate uses in regular concrete strength classes respectively for common structural elements, mainly for slabs. River sand (0/4 mm) and coarse aggregates (4/8 mm and 8/16 mm): natural sources or recycled concrete type-alternatively used in several mixes-were utilized in concrete mixes.

This paper discusses a new all–precast concrete system used in Romania to construct a residential build- ing. Designed for constructability, a new all–precast concrete system comprising columns, flat slabs, and structural walls was proposed by the design team. To validate the structural quality and performance of this type of structure, an extensive program of theoretical analyses and structural tests (including shake table tests) was conducted. The tests demonstrated good behav- ior of the precast concrete dual system (frame-wall) adapted for a classic flat-slab structure. The connections resulted in a similar behavior of the precast concrete system to that of the monolithic solution. Due to its functional and technical advantages, high productivity, and low cost, this system has been used in more than 500 flats in Transylvania, Romania.

As the demand for concrete and the needs to satisfy development of infrastructure facilities increase, it is essential to find alternatives to create environment-friendly concrete. The particular procedure of alkaline activation of fly ash - in which ash resulting from a power plant is combined with a specific alkaline activator in order to create a solid material, then dried at a certain temperature - opened new opportunities for this new material to get attention worldwide. In order to obtain a material with similar properties of ordinary Portland cement concrete and to obtain desirable compressive strengths, the parameters that affect this type of binders should be fully understood. The aim of this paper is to study the main parameters affecting the mechanical strength of the fly ash-based geopolymer paste and their interactions. Parameters such as molarity of sodium hydroxide (from 8M to 12M) and alkaline activators ratio (from 0,5 to 2,5) were analysed to observe how they affect the mechanical properties of the geopolymer paste. Experimental results show that the compressive strength of the fly ash-based geopolymer paste produced using Romanian local raw materials increases with the increase of the concentration of sodium hydroxide and higher ratios of Na2SiO3/NaOH solution.

Alkaline activation of fly ash is a particular procedure in which ash resulting from a power plant combined with a specific alkaline activator creates a solid material when dried at a certain temperature. In order to obtain desirable compressive strengths, the mix design of fly ash based geopolymer pastes should be explored comprehensively. To determine the preliminary compressive strength for fly ash based geopolymer paste using Romanian material source, various ratios of Na2SiO3 solution/ NaOH solution were produced, keeping the fly ash/alkaline activator ratio constant. All the mixes were then cured at 70 °C for 24 hours and tested at 2 and 7 days, respectively. The aim of this paper is to present the preliminary compressive strength results for producing fly ash based geopolymer paste using Romanian material sources, the effect of alkaline activators ratio on the compressive strength and studying the directions for future research.

This paper assesses the vulnerability to progressive collapse of an old and representative twelve-storey reinforced concrete (RC) framed structure, designed forty years ago for Braila according to the provisions of the Romanian Design Codes P13-70 (1970) and STAS 8000-67 (1967). The progressive collapse potential is assessed using a linear static procedure by applying damage scenarios specified in the GSA 2003 Guidelines. The results reveal that the structure has a low potential to progressive collapse based on its flexural resistance. The sensibility to shear of the old RC structure is carefully investigated and the design shear capacities are compared to experimental values furnished by static and dynamic tests.

The potential for progressive collapse of low-rise RC framed structures is evaluated in this paper. The analyses are based on the linear static procedure and acceptance criteria specified in GSA 2003 Guidelines. The main parameters of the program are the building height (three and six storeys), seismicity of the area, and the type of damage scenarios used in the analysis. The results revealed that the progressive collapse potential decreases as the number of storeys increases and, for the first time in the technical literature, demonstrates in a quantitative manner, differentiated with respect to the number of storeys, the positive effect of seismic design and detailing on the progressive collapse resistance of reinforced concrete framed structures.

Aspects of early age restrained shrinkage of concrete-induced cracking states are investigated at Romania's new Transylvania Motorway's bridge piers and abutments. General contractor Bechtel International requested the investigation, which was performed by the Technical University of Cluj-Napoca and the Cluj-Napoca branch of the National Building Research Institute (INCERC). Crack width ranges of 0.05-0.5 mm (0.002-0.02 in) were observed when the concrete was approximately one month old. Cracking state future progress analytical predictions, interpretations, and analyses are emphasized, based on general contractor-supplied technical documentation and crack width monitoring data. It was concluded that cracking states are mainly caused by restrained volume contraction within the first week because of the good match between real registered data and theoretical results. Thus, normal works progress continued, since repair measure could be done in a timely manner.

Some aspects of the behavior up to failure of reinforced and prestressed concrete elements under long-term loading (10 to 12 years), in different aggressive environments, are presented. Lightweight and normal concrete elements were exposed both in aggressive environments (chloride and nitrate pollution) and in natural environments (urban and sea). Long-term loaded elements presented cracks with a maximum width of 0.15 to 0.20 mm for reinforced concrete beams and 0.05 to 0.10 mm for prestressed beams. After 10 to 15 years, tests were performed to establish the influence of long-term aggressivity and cracking pattern on concrete durability and safety of the elements under study.