Mykhailo Ivaneiko

The paper presents the results of an experimental investigation into the stress–strain state of an reinforced concrete (RC) slab subjected to two concentrated forces. The relevance of the study is driven by the need to refine the deformation characteristics of thin slabs experiencing large deflections. The aim of the research is to analyse the evolution of strains in concrete and reinforcement at various loading stages up to failure. The digital image correlation method was employed to measure displacements and strains. The tests established that the bending moment corresponding to the attainment of the limiting deflection is Muls=1.18 kN·m; at this stage, strains in the compressed concrete zone remain at a relatively low level. Immediately prior to failure, a redistribution of deflections along the span and localisation of strains in the vicinity of one of the applied forces were recorded. The obtained results confirm the effectiveness of the DIC method for analysing the stress–strain state of RC slabs.

An accurate prediction of serviceability deflections is essential for the design and assessment of reinforced concrete floor systems. This paper presents a comparative study of the deflection response of a simply supported reinforced concrete slab obtained from a full‑scale laboratory test and from numerical simulations performed in the LIRA‑SAPR software using a step‑by‑step physically nonlinear analysis. The test specimen was a single‑span slab with a length of 3.10 m (clear span 3.00 m), width 0.50 m and thickness 60 mm, reinforced with 8 mm bars in the tension and compression zonesThe slab was loaded by six concentrated forces applied through steel traverses, which distributed each point load over a finite contact area and thus approximated an equivalent uniformly distributed load (UDL) over the span. Vertical displacements were measured at the supports using dial gauges and at midspan using an Aistov deflectometer; recorded readings were converted to relative deflections by subtracting the initial (zero‑load) values. The numerical model reproduced the experimental boundary conditions and loading stages. Two finite‑element idealizations were considered: a shell‑type model and a volumetric (solid) model, both implemented with nonlinear material laws for concrete and reinforcement available in the LIRA‑SAPR library. At each load step, the computed deflections were extracted and compared with the experimental curve. The comparison demonstrates the influence of modeling assumptions (element type, stiffness representation and nonlinear material parameters) on the predicted deflection development, especially at higher load levels where cracking and stiffness degradation become pronounced. Overall, the step‑by‑step physically nonlinear analysis in LIRA‑SAPR is shown to be suitable for reproducing the trend of deflection growth and for verifying the adopted material models against laboratory measurements. The presented methodology may be used for calibrating numerical models intended for serviceability assessment and for further studies of strengthened slab systems produced by increasing the cross‑section.

Construction requires improved principles for optimizing project durations when they deviate from normative values. To fulfill this task, it is first necessary to have information about the workflow, the composition and compatibility of work brigades, and then to apply both existing and newly developed organizational and technological methods to reduce the overall construction time. This paper proposes identifying destabilizing factors and optimization solutions for non-rhythmic construction flows. Destabilizing factors are identified both for the construction process as a whole and for its individual elements. The assessment includes deviations in labor intensity (work duration) and the presence of local and global extrema within the system. The occurrence of local minima in the construction schedule leads to downtime in the network schedule (Critical Path Method), an increase in the deployment and folding periods of work flows, and uneven consumption of labor resources. Another issue in construction is the insufficient availability of labor resources. Therefore, the task is approached through multicriteria optimization based on Pareto efficiency. To address the elimination of local minima, the article presents methods for influencing work durations and examines their impact on resource expenditure. The diagram illustrates a variant design approach for eliminating local minima. The second stage of optimization involves defining the optimization criterion and maximizing the use of similar brigades through the parallel method in the matrix system. In the parallel method, the period during which compatible brigades can work simultaneously is extended. As a result of the two-stage optimization of the non-rhythmic work flow, the following outcomes were achieved: elimination of local extrema; reduction in construction duration (from 153 to 90 days for the flow method, and from 128 to 90 days for network scheduling); nearly identical work periods for installation and integrated brigades (B – 73 days, C…D – 74 days, E – 79 days); and a reduction in the number of brigades on site (from six to five).

In the non-rhythmic flow construction of industrial facilities, there are processes with a reserve of unused labor resources on works and grabs, which affect the term of work (the period of deployment of flows). The analysis of non-rhythmic works showed that they have works with a period of curtailment of flows of greater than the smallest value and they have a reserve of unused labor resources, but do not affect the terms of execution of works. It is proposed to reduce the duration of non-rhythmic flow works on technologically identical processes by using unused labor resources on works with an increased flow curtailment period on interdependent grippers. Performed preliminary studies showed that interdependent grabs for parallel work are determined by a rank matrix with priority on the OVRR front. These jobs with increased flow deployment period showed that redistributing work volumes between two jobs reduces the duration of jobs. In previous studies, the redistribution of the volume between these two works has an abstract nature without determining the technological homogeneity of the two works. The redistribution of non-rhythmic work volumes is forged in it into technologically identical types of occupations. For processes with an increased period of curtailment of flows, it is proposed to balance two jobs by a parallel method of performing work on technologically identical types of work without the use of additional labor resources. Optimizing the reduction of the construction period involves the use of parallel methods on two technologically identical works with an increased flow curtailment period. The example shows examples of balancing two jobs by using special and universal (excavator) machines with specialized specialists or complex crews. Technical and economic indicators were determined for the performed optimization.