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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]

The paper discusses service load measurements (weight of construction materials, small equipment and workers) conducted on 120 frame scaffoldings all over Poland in 2016-2018. Despite the fact that the scaffolding should ensure the safety of its users, most accidents on construction sites are caused by fall from height. Service loads are one of the elements affecting the safety of scaffolding use. On the basis of the studies, maximum load on one platform and maximum load on a vertical scaffolding module for one day were obtained. They were treated as the random variables of the maximum values. Histograms and probability density functions were determined for these variables. The selection of a probability distribution consisted in the selection of a probability density function by means of fitting curves to the study result histograms using the method of least squares. The analysis was performed for distribution Weibull and Gumbel probability density functions which are applied for maximum values of random variables. Parameters of these functions can be used for the purposes of the reliability analysis to calibrate partial safety factors in simulation of service load during the scaffolding failure risk assessment. Besides, the probability of not exceeding the standard loads provided for frame scaffoldings for 120 weeks was established on the aforementioned basis. The results of the presented research show that in Poland there is a high probability of exceeding the permissible service loads in one year and thus there is a high risk of scaffolding damage. [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]

Abstract: The paper is concerned with the numerical analysis of a node in modular scaffolds used for construction work. The purpose of this study is to determine the capacity of a node on the basis of the numerical analysis taking into consideration two factors: nonlinear material and the interaction between particular joint elements. The main subject of the analysis are the connections between the brace and the pipe and between the ledger and the pipe of the vertical standard. The result of the analysis is the maximum load that can be applied to the elements of the node. The numerical analysis is an alternative method over traditional methods involving laboratory research. [Copyright &y& Elsevier]

The paper deals the application of the sensitivity analysis in CFD. This method is used to evaluate the influence of assumed „constants" of the standard k-e model on obtained steady flow parameters: pressure, velocity components, turbulence kinematic energy, dissipation of turbulence energy and dynamic turbulence viscosity. Differential coefficients fields of the sensitivity analysis show as the flow parameters change versus the „constants". These coefficients can be obtained from the analytical or semi-analytical direct differential methods. There are suitable formulae for described methods and exemplary results in the paper. The results of the sensitivity analysis can be useful to check the solution of CFD problems and they can be used to determine correct „constants" of the k-e model. [ABSTRACT FROM AUTHOR]

Experimental studies were performed on ringlock scaffolding joints. The most characteristic element of these joints is a rosette, which provides a temporary connection between the vertical standard and the ledger. Laboratory tests were performed using a typical testing machine and a grip handle developed by the authors, which allows loading the ringlock scaffolding joint with any type of load, regardless of the manufacturer of the scaffolding considered and the material used. A normal force, a shear force in horizontal plane, a shear force in vertical plane, a bending moment in vertical plane, a bending moment in horizontal plane, and torque were applied to the joint. The obtained data could be used to determine the load-bearing capacity of the joint, as well as the nature of the connection. In cases of bending in horizontal plane and torque, the joint should be treated as a hinge, whereas the connection is semi-rigid in case of bending in vertical plane. Four different approaches were employed for determining the joint stiffness. By analysing various modes of joint damage, critical elements could be identified, which could then be used as comparative data when analysing damages to actual structures. Additionally, laboratory tests investigating the material characteristics of individual joint elements were performed. Each joint element had different material characteristics, particularly the ledger end because it was manufactured via moulding. Unlabelled Image • Scaffolding stand-ledger ringlock joint was tested with all load forms. • The load-bearing capacity and stiffness of ringlock joint were determine. • In the case of bending in vertical plane the connection is semi-rigid. • Every element of ringlock joint has different material characteristics. [ABSTRACT FROM AUTHOR]

The main objective of the study was to estimate the mean horizontal wind action on a façade scaffolding on the basis of full-scale data. Measurements of climatic parameters were carried out for a number of façade scaffoldings (120 structures) located in Poland over a 30-month period. The measurement points were located on 2–3 deck levels of each structure and at 2–4 points placed in each level. The measurements were carried out 3–4 times during each day for 5 consecutive days. At each point, two components of wind speed were measured: first with the vane probe directed perpendicular to the façade and then parallel to the façade. Each measurement lasted 60 s, and the data were recorded every 1 s. On the basis of wind speeds, a procedure was suggested that enabled estimation of the static wind action on façade scaffoldings. The responses of structures to this action were computed via FEM simulations. The results were compared with those based on the approaches recommended by the wind and scaffolding codes. Initial analyses, illustrated by three scaffoldings without a protective cover, indicated large discrepancies between the approaches and the possibility of wind action, which is not considered in the codes. [ABSTRACT FROM AUTHOR]