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FRP composite bridges have been in operation since the mid-1990s, allowing for the evaluation of their long-term behaviour. Many of the early FRP bridges in the USA and Western Europe were equipped with monitoring systems to assess their structural integrity after years of use. In Poland, the first all-FRP composite bridge was also equipped with a modern structural health monitoring (SHM) system based on distributed fibre optic sensing (DFOS) to enable long-term performance monitoring. Over nearly a decade of use, the bridge’s strain, stiffness, and dynamic properties have been evaluated three times through static and dynamic load tests. Research findings indicate that the bridge has maintained satisfactory structural integrity and durability over an eight-year operational period. However, the quality of the adhesive joints between the girders and the deck panels was found to be inadequate, resulting in a slight decrease in the bridge’s performance, specifically in stiffness and dynamic characteristics. Fortunately, these negative changes did not compromise the bridge’s safety or serviceability, as stipulated by the design requirements. An effective repair was completed, restoring the bridge to its full operational efficiency.

This article aims to perform system identification of a nearly 30-year-old cable-stayed steel footbridge over the Wisłok River in Rzeszów (Poland). The design documentation of the bridge has been lost, and since its construction, the footbridge has been subject to renovations. The structure is highly susceptible to pedestrian traffic, and before any actions are taken to improve the comfort of use, it is necessary to create and validate a numerical model and assess the force distribution in the structure. Models are often built as mappings of an ideal structure. However, real structures are not ideal. The comparison of numerical and measured data can allow for an indication of potential damage areas. Two main purposes of the article have been formulated: (1)Development of a numerical model of an old footbridge, whose components have been degraded due to long-term use. Changes, compared to the ‘original’, focused on elongation of the cables due to rheology and a decrease in their tension. (2) Demonstrate the challenges in modeling and validating this type of bridge. In the article, the result of the numerical simulation (Finite Element Method and Ansys2024 R2 was applied, the verification was made in RFEM6) for models with different boundary conditions and varied pre-tension in cables was compared with the results of static and dynamic examination of a real object. The dynamic tests showed an uneven distribution of pre-tension in cables. The ratio of the first natural frequencies of inner cables on the north side is as high as 16%. The novelty demonstrated in the article is that static tests are insufficient for proper system identification; the same value of vertical displacement can be obtained for a selected static load, with varied tension in cables. Therefore, dynamic testing is essential. Full model updating requires a multicriteria approach, which will be made in the future.

The aim of the article is to analyze the possibilities of using a lightweight dynamic cone probe DCP to determine the quality of compaction of surface layers of embankments (from 0.10 m to approx. 0.80 m below ground level). For this purpose, comparative tests of non-cohesive soil used for the construction of embankments were carried out using the DCP test and direct tests of the degree of compaction IS in a calibration chamber with the following dimensions: height 1.10 m and diameter 0.75 m. The subsoil was prepared from difficult-to-compact sand (Sa) with a uniformity coefficient of CU = 3.10 and curvature coefficient of CC = 0.99. The soil in the laboratory in the calibration chamber was compacted in layers using a vibratory plate compactor. A database for statistical analysis was obtained, n = 68 cases described by seven variables: z, ρ, w, ρd, IS, PI, N10(DCP). It was found that the DCP probe can be used to assess the degree of compaction of embankments made of non-cohesive soil, using the developed relationship IS = f(z, N10(DCP)).

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.

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.

The purpose of this paper is to show the influence of incorrect scaffolding foundations on the stress in their elements. Static stress analysis was performed for exemplary steel façade scaffolding. The scaffolding was formed using the Plettac 70 system and was composed of 16 modules and 13 working levels. The total dimensions of the scaffolding were 45.0 × 26.36 × 0.74 m. The scaffolding was set up partly on concrete and partly on a created ground classified as coarse sand with discontinuous graining. The boundary conditions modelling the foundation considered the heterogeneity of the ground both along the scaffolding and in the direction perpendicular to the façade. The effect of uneven subsidence on the scaffolding frames was checked, adopting a constant stiffness of 3500 kN/m in half of the supports, while in the rest of them the stiffness varied from 35 to 3500 kN/m. Due to additional bending moments, normal stresses in stands and transoms of the frames increased. Incorrect scaffolding foundation has the greatest negative effect on normal forces in anchors and bracings. Because these elements are responsible for the stability of the scaffolding, their damage may result in scaffolding failure and would certainly lead to a reduction of the values of free vibration frequencies, thus resulting in the discomfort of the workers on the scaffolding and a lack of safety.

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 i th 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.

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.

The 21st century is a period of rapid development of computer technology, which allowed designers to create complex, three-dimensional models of engineering structures. Thanks to these solutions, it is possible to perform complex analyses, for example modal or dynamic ones of cable-stayed or suspension structures. For such objects, verification of the correct work of structural elements takes place in the field of non-linear analysis. The presented paper is an example of a comparative analysis concerning modal and static analysis - Natural Frequency with Nonlinear Material Models and Static Stress with Nonlinear Material Models, carried out in the Autodesk Simulation Multiphysics program with dynamic in situ tests of a suspension footbridge. The main purpose of the research was to evaluate the value of pre-tension forces in the cables of the load-bearing structure.

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.