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The crack resistance of concrete structures with low reinforcement ratios requires a broader examination. It is particularly important in the case of foundations working in changing subsoil conditions. Unfavorable phenomena occurring in the subsoil (e.g., ground subsidence, landslips, non-uniform settlement) can lead to unexpected cracking. Therefore, it is necessary to check the effectiveness of the low reinforcement provided. As there are limited studies on lightly reinforced concrete structures, we performed our own experimental investigation and numerical calculations. In the beams analyzed, the reinforcement ratio varied from 0.05% to 0.20%. It was found that crack resistance in concrete members depends on the reinforcement ratio and steel bar distribution. A comprehensive method was proposed for estimating the crack resistance of lightly reinforced concrete members in which both the reinforcement ratio and the reinforcement dispersion ratio were taken into account. Furthermore, the method considered the size effect and the fracture properties of concrete. The proposed method provides the basis for extrapolation of the test results obtained for small elements and conclusions for members with large cross-sections, such as foundations, which frequently use lightly reinforced concrete. [ABSTRACT FROM AUTHOR]

Scaffolding is equipment usually used at construction sites. A scaffolding structure is lightweight and made of elements used many times. The characteristics of scaffolding make it susceptible to dynamic actions present at the structure or occurring nearby. A scaffolding structure of medium size was subjected to analysis in this paper. The structure FEM model was loaded with single force harmonic excitation with various frequencies ranging from 1 Hz to 12 Hz applied in one of many selected points on the scaffolding façade. In the first step, natural frequencies and mode shapes of the analyzed structure were calculated. Then the full dynamic analysis was carried out to obtain maximum displacements of selected control points. The relation of excitation force frequency and location to the amplitudes of generated displacement was observed. It was found that low excitation frequencies close to the natural frequencies of the structure produced vibrations ranging to large areas of the scaffolding surface. Higher excitation frequencies are usually less propagated at the scaffolding but still may produce some discomfort to the structure users in the vicinity of the excitation force location. Scaffolding is equipment usually used at construction sites. A scaffolding structure is lightweight and made of elements used many times. The characteristics of scaffolding make it susceptible to dynamic actions present at the structure or occurring nearby. A scaffolding structure of medium size was subjected to analysis in this paper. The structure FEM model was loaded with single force harmonic excitation with various frequencies ranging from 1 Hz to 12 Hz applied in one of many selected points on the scaffolding façade. In the first step, natural frequencies and mode shapes of the analyzed structure were calculated. Then the full dynamic analysis was carried out to obtain maximum displacements of selected control points. The relation of excitation force frequency and location to the amplitudes of generated displacement was observed. It was found that low excitation frequencies close to the natural frequencies of the structure produced vibrations ranging to large areas of the scaffolding surface. Higher excitation frequencies are usually less propagated at the scaffolding but still may produce some discomfort to the structure users in the vicinity of the excitation force location. [ABSTRACT FROM AUTHOR]

Scaffoldings are used for works at height and in places that are hard to reach, which makes such works dangerous to employees and accidents occur frequently. Loads generated by scaffolding users cannot be avoided. Moving workers excite low-frequency (1–2 Hz) vibrations and scaffoldings as slender structures are prone to such dynamic action. The method for determining the probability of vibrations excitation is presented here. The quantity representing this probability is called the predictor of occurrence of a dangerous situation due to vibrations induced by a walking employee. The predictor of resonance with ith natural frequency requires an analysis of the scaffolding dynamic behavior. The frequencies and the natural mode shapes of vibrations were determined. Numerical dynamic simulations of the worker's movement on the penultimate decks of two scaffoldings were carried out, as well. Predictor analysis was made for single frequencies and combinations of frequency pairs. The predictor values calculated for the first frequency or combinations with it are the highest ones, however the probability of resonance is not only affected by the first frequency. To improve safety, the natural frequencies should be increased. For longitudinal vibrations, this can be done by adding more bracing or reducing lengths of anchors. Increasing the number of anchors gives good results in both directions. During scaffolding design of both typical and atypical constructions, one must determine the natural frequencies and then, if the first natural frequency is less than 4.0 Hz, perform a dynamic scaffolding analysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new method of measuring axial forces in façade scaffolding standards. • A new method for examining the path of vertical load transfer from the scaffolding to the ground. • Description of irregularities in the scaffolding based on measurements of axial forces. • Practical examples of using the presented research methods. • Critical evaluation of 115 scaffoldings, tested on construction sites in 2016–2018. The paper presents a new research method for measuring axial forces in scaffolding on a construction site in difficult measurement conditions, consisting of a device, a measurement procedure and a mathematical apparatus for analysing the results. The paper describes the method of evaluating errors in a new type of measurement and methods of avoiding these errors in the analysis of results. The studies were performed on 115 scaffolds. The results analysis included checking the reliability of the results and the rules for their rejection, research of the load uniformity acting on mudsills, and checking whether the anchors are subjected to vertical forces transmitted from the scaffolding. The research results showed that the most of scaffolds did not work properly. The structure instability or incorrect foundation on the ground can cause the measurement results to be unreliable. The described research method may be used in Structural Health Monitoring in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • The method for assessing the technical conditions of scaffolds used on construction sites. • Inventory of scaffolds and full-scale measurements of their loads. • Finite elements static analyses of scaffolds which are subjected to real loads. • Scenarios of scaffolding failures. • The probability of a scaffold failure at maximum loads. The paper presents a method of determination for the probability of a scaffold failure at maximum loads which are measured in one week. The research concerns scaffolding which were used on construction sites. The method assumes that the geometries (including imperfections) are deterministic and are compliant with the conditions measured on the construction site. The material properties of the scaffolding components, which cannot be measured, are generated from the normal distribution. Failure is treated as a random event occurring when one component or a group of components fails. The failure event is described by a set of serial diagrams concerning stands, transoms, and additional elements, as well as a mixed diagram concerning a wall anchoring. Probabilities of a failure were determined for 120 scaffolding and their values were obtained in a range from 10-9 to almost 100. A positive or negative evaluation of the scaffolding depends on the level of the acceptable risk of failure. If reliability predictor (parameter similar to reliability index) is equal to 4.7, 41% of the scaffolds used for 12 weeks do not ensure safety of construction workers. If the reliability predictor is equal to 3.5, the percentage of unsafe scaffolds is 17%. The presented results concern frame scaffolds, erected next to elevations and forming planes. It is probable that for frame scaffolds with more complex geometries and modular scaffolds, the results will be different. [ABSTRACT FROM AUTHOR]