Volume 67 (2021): Issue 2 (June 2021)

The paper presents the main mathematical relationships for the evaluation of the compressive strength of Portland cement concretes made over time by researchers of worldwide recognized scientific value. The authors use in their relations the influence factors on the value of the compressive strength and the conditions that the components of the concrete must meet. Each mathematical relation was verified by the authors through complex laboratory research and by imposing restrictive conditions for achieving the mechanical performance and durability of the studied concrete. It presents the advantages, disadvantages and scope of use of relations, as well as the possibilities for their application for the present. The relationship established by Feret in 1892 (also reformulated by him in 1896) is a qualitative relationship, which takes into account the absolute volumes occupied by cement, water, occluded air and the quality of the cement; the relationship established by Bolomey in 1935 and completed by the Russian scholar Skramtaev is a quantitative relation, which takes into account the dosages of cement, water and the quality of cement and aggregates. Feret’s relationship, updated in 1999 by François de Larrard, as well as Bolomey’s relationship, updated in 1979 by Dreux-Gorisse, proved their validity and usefulness in evaluating the mechanical performance of Portland cement concrete.

Concrete is a building material with a continuous demand in the construction industry due to the convenient price-performance ratio. On the other hand, concrete is not an environmentally friendly material. Thus, in order to obtain a sustainable material, wood waste can be recycled and used as light aggregates in the manufacture of precast ecological building blocks. Block walls must satisfy not only structural criteria but also functional requirements. In addition, thermal contribution is important in reducing energy consumption over the life of the building. The presence of moisture on the exterior walls due to the appearance of condensation will decrease the thermal performance of building materials. This paper analyses the occurring of condensation risk and its location in the outer wall made of wood-concrete blocks by the Glaser method, for different situations of arrangement and composition of the layers.

Due to the need of sustainable development of the building sector, it is important to increase the energy efficiency in buildings and reduce the energy consumption for heating and cooling. In a changing world, full of innovative solutions and technologies, passive strategies of vernacular architecture are more used to achieve life quality and eliminate the negative impact on the environment and human health.

The vernacular architecture is based on the local construction materials and influenced by the traditions, culture and climate of the place. The “architecture without architect”, used mainly in housing, evolves over time and reflects the level of technology and historical context of the building. The core of this type of buildings was to use architecture to collect free energy from natural environment.

Demonstrated over time, the inherent and timeless knowledge of vernacular architecture offers the basic level of comfortable living without the active strategies that include technologies. Passive architecture strategies are defined by minimizing or avoiding the energy consumption, using architecture and the natural environment to produce heating, cooling, ventilation and light. The elements of the natural environment are the sources of the energy: the sun, the earth, the air – the wind, the water. By adding active technologies, the quality of living must increase, but without influencing the main resources gained through passive strategies.

The present paper will provide the information needed to understand the importance of the vernacular architecture’s passive strategies, as well as describe a few examples of those strategies in different parts of the world, examples that demonstrate the efficiency and the impact of these systems. The authors state that the use of those strategies in the first stage of architecture design helps to achieve easier the energy efficiency required nowadays and represents the fundamental base for passive houses and nearly zero energy buildings.

Religious art, expressed through the architecture and painting of churches, is subject to the action of time, requiring preservation of the architectural and artistic heritage throughout their existence by providing adequate microclimate parameters.

Functional and constructive particularities of cult buildings – large volumes constructed, high thermal inertia of the envelope elements and periodically occupied spaces with variable occupant – influence the conditions of conformation and operation of the heating and air conditioning systems.

The determination of the calculation parameters and the conformation of the installation systems must take into account these particularities and consequences leading to the necessity to provide some installations with low functional inertia.

The report presents an adequate method of calculation based on the thermal balance of the air in the enclosure and the envelope space, under the conditions of cyclical operation and with limited duration of the installations.

The paper is within the thematic context of the doctoral thesis “Energy efficiency solutions for heritage buildings”

The implementation of the cutting-edge technologies - related to communication and information transfer, as well as those related to intelligent materials, sensors, components and modules represent the only plausible way towards the emergence of complex, autonomous and decentralized systems of adaptation. The adaptive architecture deals with buildings designed to adjust dynamically to the environment, inhabitants and contained objects, its behaviour being influenced by the response of the users and the environment. The author highlights the innovations and adaptive capacities currently available by critically examining the specialized literature, by showing the philosophy behind the design of adaptive architecture - the direct involvement of the user in the act of designing and personalizing the adaptive architectural space, a continuous optimization process, in real time, by using it. The research results indicate that the emergence of adaptive architecture is based on the continuous cultural and technological remodelling of the contemporary ethos; the built environment influences the cognitive level, the emotions, the mental and physical well-being. The processual dimension, conferred by technology, allows for the possibility of manifesting an autonomous behaviour, capable of alternating the organization of the space, thus outlining a framework well suited to user’s searches.

Building integrated photovoltaics (BIPVs) are modern photovoltaic (PV) modules which are integrated into the building’s envelope. Usually, these devices replace the conventional roofing system, but they may be also integrated into the facade. The modules integration has a significant advantage in limiting the overall cost of the construction. Furthermore, building integrated photovoltaics, in comparison to non-integrated ones, don’t require stand-alone systems or allocation of land. This paper presents the state-of-the-art review regarding the existing BIPVs technologies. Also, in the second part of the paper, future research directions are discussed.

Joints made out of tubular steel members are often used in industrial constructions, like offshore, trusses or tree-shaped columns. The joint area is the weakest point in a truss structure. Beside the normal static behaviour many non-linearities due to the geometry or to the welding process have to take into account. Steel hollow sections are often used. Much research was made on welded nodes so far, but mostly it is valid for limited geometries or load cases. A review of the main aspects in designing welded nodes are given.

The second part is about a study of two aspects. The first aim is to investigate the influence of the joint angle on the resistance of a T-joint made out of Circular-Hollow-Sections or Squared-Hollow-Sections under a tensional load. To archive the most realistic results, the second aspect, a numerical study on the finite element types and the element shape functions will be made.

The phenomenon of shear lag refers to the increases of the bending stresses near the flange-to-web junctions, and the corresponding decreases in the flange stresses away from these junctions.

In the plated structures with wide flanges, such as in the orthotropic deck of the steel road bridges, shear lag caused by shear strains, may be taken into account by a reduced flange width concentrated along the webs of the steel plate girders.

In the norm EN 1993-1-5, the concept of taking shear lag into account is based on effective^s width of the flange which is defined in order to have the same total normal force in the gross flange subjected to the real transverse stress distribution as the effective flange subjected to a uniform stress equal to the maximum stress of the real transverse distribution.

This paper presents some aspects concerning the shear lag phenomenon and a design analysis taking into account the geometrical parameters such as the stiffeners thickness, flange width and the girder span for a steel deck of a road bridge.

Concrete is one of the most used construction materials but there is also the need to continuously improve it. The high consumption of natural resources and energy when manufacturing cement demand a “greener” approach. One possibility is to partially replace the cement with other admixtures, transforming the material into a more ecological version. In the present paper is also continued the experimental analysis of the possibility to embed various textile structures with a modified mineral matrix.

In this paper are presented different approaches of microbiological type, on the concrete matrix, that has the ability to self-healing the micro-cracks in their early phase. Although the prevention of cracks in the concrete structure is not possible, there are many types of techniques that will lead to self-sealing. Thereby we can say the cracks represent the biggest enemy of the elements in the constructions, and if they are not observed and treated in the early phase, they can create real dangers, both for the constructions and for the people. The micro-cracks appeared in the concrete matrix are determined by a number of internal and / or external factors. The determination of the cause of the appearance of the micro-cracks is done by visual inspections and by direct measurements, using special equipment. The identification of the various biological compounds and their use in autonomous processes can represent a sustainable but also efficient alternative on the costs of concrete production. From the researchers’ reports, the application of chemicals and polymers represents a source of risks for human health, plus the fact that these methods are viable in the short term.

The bio products exemplified in this paper are found in nature, are human friendly, and through the information provided by the researchers we can say that they increase the life of the construction. An important feature of the use of organic products in the concrete matrix is the fact that the concrete can self-healing, only needing water and oxygen. The two approaches of autonomous type presented in this paper are similar in terms of the result obtained but different from the point of view of the healing agents used. This paper will provide an overview of the bio approach through the production of calcium carbonate, will present the new challenges for sealing the micro-cracks and recommendations for future research.