Seismic design of NPP structures taking into account foundation slab compliance

The present article proposes a mathematical method for factoring in the compliance of foundation slabs in NPP structures under dynamic loading. In many cases, such an approach allows the analysis results to be significantly improved, whereas sometimes it is simply a necessary part of the procedure, i.e., when structures having “detached” exterior walls are exposed to an air shock wave generated by an aircraft crash.The presented method applies soil springs and dampers as per ASCE 4-16, specially distributed along the foundation slab bottom of a building.The conclusion presents the results of calculating the integral characteristics of soil springs and dampers according to the realistic (saddle-shaped) law of their distribution along the foundation slab bottom of a typical building.

PIPE-CONCRETE CENTRALLY-LOADED SUB-COLUMN OF A STEEL COLUMN FOUNDATION

A new progressive solution is considered, which consists in improving the design and static calculation of the strength of the elements of the sub-column part of a pipe-concrete foundation, in simplifying the design of a sub-column made of structural concrete of increased and high strength and a thin-walled metal pipe, using it in the form of a permanent formwork as a working element of a composite structure, in reduction of labor intensity and terms of performance of works of the zero cycle. An algorithm is proposed for designing elements of a precast-monolithic reinforced concrete foundation for a column, including a pipe-concrete sub-column, its fl ange connection with a steel column from above and with a foundation slab from below. Thin-walled pipe metal is an economical casing for in-situ concrete.

Underfloor Heating Using Room Air Conditioners with Air Source Heat Pump in a Foundation Insulation House

A good thermal environment is important in a place where occupants stay for a long time. Since heating a house consumes a lot of energy, an energy-efficient heating method will be required. Then, by combining a heat pump and underfloor heating, there is a possibility that both thermal comfort and energy saving can be achieved. The survey was conducted on a detached house located in Nagano Prefecture, Japan. The average outside air temperature was 4.2 °C. This study investigated the indoor thermal environment, evaluated the operating performance of the heat pump, and calculated the heat load by two-dimensional analysis. More than 80% of the subjects were satisfied with the thermal environment and the neutral temperature was 18.9 °C. In the operation of the heat pump, defrost operation was confirmed, but the average COP was 2.9, and it operated efficiently. In addition, the heat loss from the foundation slab was examined. Proper insulation placement has shown the potential to reduce heat loss. In conclusion, the use of heat pumps as a heat source has been shown to be efficient even in cold climates, and this study supports the construction of new heating methods.

Self-Compacting Concrete and Concreting Technology for Foundation Block Using 9000 Cubic Meters of Concrete

. The paper presents the results of the development and implementation of the technology of self-compacting heavy structural concrete and the technology of concreting with its use of the largest foundation slab in Belarus (concrete volume ~9100 m3) of a high-rise building at the facility “Construction of a multifunctional complex in Minsk within the boundaries of Filimonova Street – Avenue Nezavisimosty – Makayonka Street”. The results of research are shown, which ensured the production of self-compacting concrete of class C35/45 with water resistance up to W20 (with the required W12 according to the project) from concrete mixtures of the maximum cone expansion of the PK6 (RK6) grade for three zones of the foundation slab different in degree of reinforcement: lower, middle and upper, with a total structure height of 3.5 m and plan dimensions ~(83´34) m. The technology of continuous (seamless) concreting has been developed and implemented, which made it possible to lay ~9100 m3 of concrete into the structure without defects within 42 hours of continuous operation, and a system of technological measures that prevented temperature cracking in concrete. The homogeneity of the physical and mechanical properties of concrete, confirmed by control tests, is ensured due to the uniform supply of the concrete mixture (from six concrete pumps at the same time) in layers 200–300 mm high with a distance between the supply points of about 5–6 m and the vertical arrangement of the “trunks” of the concrete pipes during delivery of concrete to each point, as well as the fact that the time for feeding the next volume of concrete was significantly less than the setting time of the previously laid concrete (with a total concreting speed £0.1 m/h). Standardized and original test methods for concrete mixtures, hardening kinetics and properties of hardened concrete have been used during the development, research and implementation of the project. Control tests of physical and mechanical properties and characteristics of concrete, carried out at BNTU together with authorized organizations controlling the progress of construction, as well as in independent (third-party) organizations, have confirmed their compliance with the design requirements.

Assessment of Thermally Stressed State of Concrete Massif

The paper describes a technique for assessing the thermally stressed state of a concrete massif of a foundation slab made of a self-compacting concrete mixture. The proposed method consists in a preliminary calculation of temperature fields in hardening concrete. The objects of research have been self-compacting concrete mix and structural concrete in the structure mass. The choice of materials for the preparation of a concrete mixture is given and substantiated. The composition of self-compacting concrete has been used to assess the thermally stressed state. A binder with a reduced exotherm has been used in order to reduce the self-heating of concrete. Studies have been carried out to assess the specific heat release of the recommended cement depending on the initial water-cement ratio. The effect of a chemical additive on the rate and magnitude of the specific heat release of cement has been studied. The paper presents the main theoretical provisions and an algorithm for calculating the thermal stress state of a concrete massif. The finite difference method has been used to calculate the expected temperatures and their distribution in the structure mass, and the temperature stresses in the sections of the concrete mass have been calculated to assess the thermally stressed state. The performed calculations of the temperature fields have made it possible to estimate the maximum possible temperatures and temperature differences over the sections of the concrete massif depending on the initial temperature of the concrete mixture and the average daily temperature of the outside air. Analysis of the temperature distribution has revealed the most dangerous sections of the concrete mass. An assessment of the thermal stress state of the concrete mass has been made on the basis of the results pertaining to calculation of temperature fields. The calculation of temperature stresses in the most dangerous sections of the concrete massif has been performed. It is shown that the calculated value of the temperature stress can serve as a characteristic of the thermally stressed state of the concrete mass. The formation of temperature cracks in a concrete mass is possible when the calculated value of the temperature stress exceeds the actual tensile strength of concrete. Comparison of the calculated and actual values of temperatures in the sections of the foundation slab has made it possible to conclude that the calculations of the temperature fields and, as a consequence, possible temperature deformations are correct.

Records of Extreme Ground Accelerations during the 2011 Christchurch Earthquake Sequence Contaminated by a Nonlinear, Soil–Structure Interaction

ABSTRACT Ground-motion records are critical for seismic hazard assessment and seismic design of buildings and infrastructures. Large (>1g), asymmetric vertical accelerations (AsVAs) have been observed at strong-motion stations during recent earthquakes. However, it is not clear whether all of the observed AsVAs reflect actual ground shaking or the interaction of a building structure and underlying ground. Here, we investigate the cause of large AsVAs recorded at several seismic stations in Christchurch, New Zealand, during the 2011 Mw 6.2 Christchurch earthquake. We first define three metrics and quantify the degree of waveform asymmetry in all available records from nearby M>3 earthquakes. Histograms of the metrics show greater waveform asymmetry for larger accelerations at these stations, which is consistent with the prediction of a nonlinear, soil–structure interaction associated with the elastic collisions of a foundation slab onto the underlying soil. We then use finite-element models to examine the occurrence of the nonlinear, soil–structure interaction at these stations during the Mw 6.2 mainshock and Mw 5.6 aftershock of the 2011 Christchurch earthquake. The parameters of the numerical models are constrained by site investigation of selected stations. We find that numerical simulations closely reproduce the large AsVAs recorded at stations HVSC and PRPC, suggesting that these ground-motion records were contaminated by the nonlinear, soil–structure interaction. Seismic sensors located near the corner of a concrete slab are shown to be more prone to this phenomenon. Our results further suggest that artificial recording of large AsVAs due to the nonlinear, soil–structure interaction can be mitigated if a seismic sensor is placed closer to the center of a foundation slab. The analytical procedure presented in this study may be useful in identifying the occurrence of AsVAs elsewhere and in assessing whether AsVAs are caused by the nonlinear, soil–structure interaction.

Modeling of foundation slabs of buildings on complex foundations

The paper considers the problem of calculating the strength of foundation slabs under seismic and wind loads. As an example, a numerical model of a hotel building to be built on bulk islands is presented. The calculation of the foundation slab model is performed using the STARK ES software package. The results of the calculation are analyzed and recommendations for strengthening the foundation are given.

Analysis of the application efficiency of the slab-pile foundation using the example of a two-layer base

The purpose of this work was to determine the increase of the limit load when resting the foundation slab on the ground at a different pitch of piles and their different length. The main task is to calculate the combined pile-slab foundation. The hypothesis was that when the foundation slab in the work, the bearing capacity of the entire structure increases. This foundation was calculated using the Plaxis 3D design software complex. In this article, we have determined the value by which the ultimate load on the combined pile-slab foundation increases when the slab rests on soil.

Formation of stress-strain state in the founda-tions of grain drying complexes when chang-ing soil parameters

The work of the pile foundation of the grain drying complex when changing the parameters of soils determined by laboratory and field methods has been studied. Two variants of calculations with the help of numerical modeling by the finite element method were carried out: 1) using the characteristics of soils, which were determined by laboratory methods; 2) using the characteristics of soils, which are determined by field methods. The stress-strain state of the foundation structures of the grain drying complex is analyzed in the work, namely: redistribution of forces in the piles, subsidence of the foundation structures, bending moments and the area of working reinforcement in the foundation slab. The paper emphasizes the use of pile foundations for grain drying complexes due to the emergence of many negative factors in the installation of slab foundations. The main ones are: low soil indicators in the upper zone of the soil massif; construction of several silos next to each other, which determines their interaction; uneven loading - unloading of silos; the choice of calculation method, which correctly describes the parameters of the soil and the stages of loading and unloading of silos. The paper also presents problematic issues in the design of pile foundations for grain dryers. The results of the study of the formation of the stress-strain state of the foundation structures at different soil parameters are presented. The study was conducted in clay soils of solid and semi-solid consistency. The pile foundation is based on hard sandy loams and soft-plastic loams. The paper shows that with increasing soil parameters of the base decreases the subsidence of the foundation slab. The redistribution of forces between the piles has a similar character, but due to the increased rigidity of the base, the foundation plate transfers the load to the base, so almost all piles are unloaded within 5… 10%. At the same time bending moments in the base plate are reduced that demands reduction of reinforcement by working armature. This allows you to design reliable and economical solutions for pile foundations of grain dryers.