EXPERIMENTAL STUDY OF THE OPERATIONAL PERFORMANCE OF LOAD-BEARING AND ENCLOSING STRUCTURES IN MONOLITHIC AND PRECAST-MONOLITHIC CIVIL BUILDINGS

ABSTRACT

The aim of this study was to compare the operational performance of load-bearing and enclosing structures in monolithic and precast-monolithic civil buildings under service conditions. Laboratory tests were used to assess service deflection, stabilized crack width, residual deformation, thermal resistance, water absorption, and defect sensitivity. The monolithic series showed lower service deflection (6.8 mm versus 8.1 mm), smaller crack width (0.18 mm versus 0.24 mm), and higher thermal resistance (3.42 versus 3.08 m²·°C/W). Precast-monolithic solutions also demonstrated acceptable behavior, but they were more sensitive to joint quality, insulation discontinuity, and sealing defects. The study formulates practical recommendations for joint detailing, curing control, interface sealing, and improvement of thermal continuity.

АННОТАЦИЯ

Целью исследования являлось сравнительное изучение эксплуатационных характеристик несущих и ограждающих конструкций монолитных и сборно-монолитных гражданских зданий в условиях эксплуатационных воздействий. В ходе лабораторных испытаний оценивались прогибы при эксплуатационной нагрузке, стабилизированная ширина раскрытия трещин, остаточные деформации, тепловое сопротивление, водопоглощение и чувствительность к дефектам. Установлено, что монолитная серия характеризуется меньшими прогибами (6,8 мм против 8,1 мм), меньшей шириной трещин (0,18 мм против 0,24 мм) и более высоким тепловым сопротивлением (3,42 против 3,08 м²·°C/Вт). Сборно-монолитные решения также обеспечивают приемлемую работоспособность, однако в большей степени зависят от качества стыков, непрерывности теплоизоляции и герметизации сопряжений. Сформулированы практические рекомендации по узловым решениям, режимам твердения, герметизации интерфейсов и обеспечению теплотехнической непрерывности.

Keywords: monolithic buildings, precast-monolithic systems, load-bearing structures, enclosing structures, operational performance, crack resistance, thermal resistance, durability, civil buildings.

Ключевые слова: монолитные здания, сборно-монолитные системы, несущие конструкции, ограждающие конструкции, эксплуатационные характеристики, трещиностойкость, тепловое сопротивление, долговечность, гражданские здания.

1. Introduction. The development of civil construction increasingly depends on structural systems that combine bearing capacity, durability, maintainability, and energy efficiency throughout the service life of a building. In this context, monolithic and precast-monolithic reinforced-concrete schemes are widely used because they allow flexible planning solutions, high structural rigidity, and relatively efficient organization of construction processes [1–5].

At the same time, the operational quality of a building cannot be reduced to the design strength of its frame alone. Load-bearing structures are assessed by stiffness, crack resistance, residual deformation, continuity of force transmission, and long-term reliability, whereas enclosing structures must additionally preserve thermal resistance, moisture stability, airtightness, and surface durability under fluctuating temperature and humidity conditions [3, 5, 7, 8].

In practice, these two subsystems operate as a unified envelope-frame complex. Defects in joints, slab edges, wall interfaces, and insulation layers may simultaneously reduce structural reliability, increase heat losses, intensify moisture penetration, and accelerate maintenance needs. For monolithic systems, the main advantage is the continuity of concreting and reinforcement anchorage, while precast-monolithic systems depend to a much greater extent on the quality of interfaces between prefabricated and cast-in-place elements.

The aim of this study was to experimentally compare the operational performance of load-bearing and enclosing structures in monolithic and precast-monolithic civil buildings and to formulate engineering recommendations for improving their reliability, durability, and energy efficiency in service. The scientific novelty of the work lies in the integrated assessment of structural and enclosing elements within one operational framework rather than in separate isolated evaluations.

2. Materials and Methods. The experimental program covered two groups of structural solutions. Group A represented monolithic load-bearing and enclosing structures executed primarily by cast-in-place reinforced-concrete technology. Group B represented precast-monolithic solutions formed by prefabricated reinforced-concrete elements combined with cast-in-place joints, topping layers, diaphragms, and local monolithic inserts. For both groups, comparable slab fragments, wall-node fragments, and enclosing wall assemblies were selected.

The assessment focused on indicators that are directly related to operational performance under service conditions. For load-bearing elements, the study considered compressive strength of concrete, service deflection, stabilized crack width, and residual deformation after repeated loading. For enclosing structures, the assessment included thermal resistance, water absorption after cyclic wetting and drying, and an integral defect sensitivity index characterizing the tendency of the assembly to form local thermal bridges, moisture stains, and surface defects.

Mechanical loading was applied stepwise with the registration of deformation and crack development at each stage. Crack widths were measured in the most stressed sections and especially in interface zones. Thermal resistance was evaluated for wall fragments with insulation and finishing layers in accordance with calculation principles adopted for building envelope assessment [7]. Moisture stability was examined by wet-dry cycling followed by mass measurements and visual inspection of the surface condition. The interpretation was deliberately focused on service-level behavior rather than ultimate failure in order to identify the conditions that most strongly affect the long-term operational suitability of the building.

Table 1.

 Experimental program and evaluated indicators

3. Results. The experimental results indicate that monolithic load-bearing elements demonstrate higher integral rigidity and lower average service deflection than comparable precast-monolithic elements. Stabilized crack width in the monolithic series remained smaller, which points to a more uniform distribution of tensile strains. Residual deformation after repeated loading was also lower, indicating reduced accumulation of operational damage.

The precast-monolithic series showed satisfactory behavior overall, but its performance was more sensitive to the quality of joints and to the compatibility of stiffness between prefabricated and cast-in-place parts. The most critical zones were the interfaces where local stress concentrations provoked earlier crack initiation. When node reinforcement, interface preparation, and compaction quality were improved, the difference between the two systems narrowed but did not disappear completely.

For enclosing structures, monolithic walls demonstrated a more stable thermal contour and lower moisture accumulation. Precast-monolithic envelopes were characterized by greater variability of thermal resistance because of joints, embedded elements, and local discontinuities in the insulation layer. The highest defect sensitivity in both systems was associated with incomplete sealing, slab-edge thermal bridges, and moisture penetration into the joint zones.

Table 2.

Comparative results for load-bearing structures

Figure 1. Comparison of average service deflection of slab fragments

Figure 2. Comparison of stabilized crack width in load-bearing elements

Table 3.

 Comparative results for enclosing structures

Figure 3. Thermal resistance of enclosing structures

4. Discussion. The comparison confirms that the operational advantage of monolithic structures is primarily associated with continuity. Continuous concreting and reinforcement anchorage reduce the number of mechanically and thermally vulnerable interfaces, support more uniform redistribution of local stresses, and improve crack control. This, in turn, reduces the probability of moisture penetration and the initiation of corrosion-related damage [1–6].

However, the results do not suggest that precast-monolithic systems are unsuitable for civil buildings. Their main strength lies in technological flexibility, shorter erection time, and the possibility of industrialized production of individual components. The decisive engineering requirement is the reliable design and execution of joints: adequate shear transfer, surface preparation of precast elements, reinforcement continuity, and elimination of insulation discontinuities in slab-edge and connection zones [4–8].

From the standpoint of operation, enclosing structures are no less important than the load-bearing frame. Even where strength criteria are satisfied, insufficiently sealed interfaces and local thermal bridges may lead to condensation, increased heat losses, finishing defects, and a deterioration of indoor environmental quality. For this reason, quality control at the construction and commissioning stages should assess the structural frame and the building envelope as one integrated system.

5. Conclusion. The experimental study established that monolithic civil buildings generally provide better operational performance of load-bearing structures in terms of stiffness, crack resistance, and residual deformation. The monolithic series also demonstrated better thermal continuity and lower moisture sensitivity in the enclosing structures.

Precast-monolithic systems preserve important organizational and technological advantages, but their long-term operational reliability depends more strongly on the quality of joints between prefabricated and cast-in-place components, as well as on the continuity of insulation and sealing in the enclosure system.

The practical significance of the work lies in the proposed measures for improving joint detailing, curing discipline, sealing of interfaces, and thermal continuity control during construction and commissioning. The revised manuscript therefore considers the frame and envelope not as separate fragments of the building, but as a unified operational complex that determines serviceability, durability, and energy efficiency.

References:

1. Neville A. M. Properties of Concrete. 5th ed. Harlow: Pearson Education Limited; 2011.
2. Mehta P. K., Monteiro P. J. M. Concrete: Microstructure, Properties, and Materials. 4th ed. New York: McGraw-Hill Education; 2014.
3. fib. fib Model Code for Concrete Structures 2010. First ed. Berlin: Ernst & Sohn; 2013.
4. BS EN 1992-1-1:2004+A1:2014. Eurocode 2: Design of Concrete Structures — Part 1-1: General Rules and Rules for Buildings. London: BSI; 2014.
5. ACI Committee 318. Building Code Requirements for Structural Concrete (ACI 318-19) and Commentary. Farmington Hills, MI: American Concrete Institute; 2019.
6. ACI Committee 437.2. Load Testing of Concrete Structures — Code and Commentary (ACI CODE-437.2-22). Farmington Hills, MI: American Concrete Institute; 2022.
7. ISO 6946:2017. Building Components and Building Elements — Thermal Resistance and Thermal Transmittance — Calculation Methods. Geneva: International Organization for Standardization; 2017.
8. ISO 13788:2012. Hygrothermal Performance of Building Components and Building Elements — Internal Surface Temperature to Avoid Critical Surface Humidity and Interstitial Condensation — Calculation Methods. Geneva: International Organization for Standardization; 2012.