The design of vertical formwork is governed by the lateral pressure exerted by fresh concrete; while maximum lateral pressure is the key parameter for formwork design, the pressure stabilization time is important for determining formwork removal time. This work describes an experimental study of columns made with self-compacting concrete (SCC) to determine the variation in the maximum lateral pressure and the pressure stabilization time with the following variables: concrete temperature and the presence of different reinforcement densities. Maturity functions and their relationship to the resistance acquired by the concrete over time were studied in order to determine the minimum times for formwork removal. The results show that SCC temperatures have an inverse relationship with the lateral pressure of fresh concrete, and the influence of reinforcement on the maximum lateral pressure depends on the number of steel bars and their arrangement; moreover, the lateral pressure of fresh concrete has no influence on the pressure stabilization time. Finally, a formwork removal method based on the maturity index was proposed. (C) 2015 Elsevier Ltd. All rights reserved.

In construction practice, an accurate model to predict fresh concrete lateral pressure is needed in order to design vertical formwork. In this work, an empirical model to predict lateral pressure for vibrated concrete was developed. A total of 226 experimental data recompiled from the literature were used in the formulation of the model. The model considers seven of the variables that affect fresh concrete lateral pressure: placement rate, slump cone, the height of the concrete piece, concrete temperature, minimum form dimension and cross section size. Due to the formulation of the model, the prediction obtained is always lower than the hydrostatic distribution. The principal objective of the model is to have an accurate prediction for high placement rates (over 10 m/h), which is a common practice today. Based on this idea, experimental data for self-compacting concrete compiled from the literature were used to verify the model's accuracy. The results show that, in general, applying the proposed model produces predictions that are better than those obtained from preexisting models. In particular, for high placement rates the model presents a very good approximation to the experimental data. (C) 2013 Elsevier Ltd. All rights reserved.

The design of vertical formworks is governed by the lateral pressure exerted by fresh concrete; while maximum lateral pressure is the key parameter for formwork design, the rate of pressure decay and the time needed for pressure stabilization is important for determining formwork removal time; the complexity of the problem is due the large number of factors which affect the rate of pressure decay. This works describes an experimental investigation of columns to determine the variation in the initial lateral pressure decay and in the time needed for pressure stabilization with the following variables: coarse aggregate concentration (different sand to total aggregate ratios were used), the use of a plasticizer, the presences of reinforcement and concrete temperature. In the last part of this work a correlation between setting time and maturity functions with the time needed for pressure stabilization was done. The results show that both thixotropic linked to cement grains nucleation and consolidation and cement hydration influences in lateral pressure decay to the point of stabilization. In references with the initial pressure decay, the presence of reinforcement seems to have a major influence. On the other hand the time needed for pressure stabilization could be correlated with the maturity functions. (C) 2013 Elsevier Ltd. All rights reserved.

Although there is a great deal of papers on single-layer latticed structures, practically the totality of them is devoted to domes. Therefore, the authors have chosen to analyse squared plan-form single-layer structures studying the influence of joint-rigidity, mesh-density, rise-to-span ratio and load combination in their behaviour, through a Design of Experiments analysis. After identifying the most influential parameters, more FEM analyses were run resulting in interesting conclusions which included economic considerations. The influence of initial imperfections was also investigated. (C) 2011 Elsevier Ltd. All rights reserved.

The design of vertical formwork is governed by the lateral pressure exerted by fresh concrete; the complexity of the problem is due to the large number of factors which affect pressure. This work describes an experimental investigation in columns to determine the variation in lateral pressure and initial rate of pressure drop with the following variables: formwork size and shape, coarse aggregate concentration and concrete temperature. An 8-run factorial design 23 was done to determine the influence of formwork size and shape and coarse aggregate concentration. It was impossible to vary temperature between two levels in the field, so in this analysis this factor was considered as a co-variable. With this objective, square and circular experimental columns 3 m high but with different cross sections were instrumented, and two concrete mixtures with different sand to total aggregate ratios were used. Afterwards, two tests were done to determine the influence in pressure of concrete impact, changing the method for filling the columns. Formwork shape, coarse aggregate concentration and concrete impact have a minor effect in maximum lateral pressure, while temperature shows an inverse relationship with the pressure, but not to a sufficient degree to be considered a significant parameter. On the other hand, formwork size has a major effect on the pressure, narrow sections generate less lateral pressure than higher ones. This is attributed to the friction forces between concrete and formwork which are much more important in small sections. Formwork shape and size present a major influence in the initial rate of pressure decay. While circular formworks present a higher value than squares ones, smaller cross sections present a lower value than larger ones. On the other hand, coarse aggregate concentration has a minor effect on this parameter. (C) 2010 Elsevier Ltd. All rights reserved.

In the design of single-layer structures, the hypothesis of pinned joints leads to structures with low capacity in terms of stability and resistance. Therefore, one of the main concerns of structural designers in recent years has been to find an appropriate joint design which would endow the joint with sufficient stiffness. In this paper, the results of experimental tests conducted with the aim of establishing geometrical parameters for a semi-rigid joint that may be used in single-layer structures are presented. They showed how the combination of different parameters can improve the stiffness of the joint and its rotational capacity. At the same time, the experimental tests provided the initial rotational stiffness of the tested joints which is to be introduced into the analysis of the structure. The paper presents an analytical method for the determination of the initial rotational stiffness of the joint. The method follows a technique similar to the component method of Eurocode 3 part 1.8, although it has been adapted to the geometry of this particular joint. (C) 2010 Elsevier Ltd. All rights reserved.

An analysis of experimental models for predicting fresh concrete lateral pressure in walls and bases was carried out, including a comparison of three rate of placements. Experimental data obtained from the bibliography were used for comparing the adequacy of the models, making a division into three placement rates ranges: under 2 m/h, between 2 m/h and 10 m/h and over 10 m/h. The comparisons were established not only in the different ranges but also taking into account the level of construction control, vigilance and inspection, considering in all cases safety and adequacy for better formwork design. The influence of concrete yield stress, evaluated from slump test, is also analyzed; the study shows a low correlation between concrete yield stress and the ratio maximum pressure vs. hydrostatic pressure for low rates of placement. On the other hand for higher rates of placement, the correlation increases. (C) 2010 Elsevier Ltd. All rights reserved.

El diseño de encofrados verticales depende de la predicción de la presión lateral contra las paredes del mismo, debido a la forma que presenta la envolvente de la presión lateral es difícil poder realizar una validación de los modelos experimentales solamente utilizando parámetros estadísticos. Por lo tanto, este artículo tiene dos objetivos fundamentales, en primer lugar busca explicar porque cocientes entre datos experimentales y teóricos (E/T) mayores que uno pueden ser aceptados a la hora de validar un modelo, y en segundo lugar cuantificar el máximo cociente E/T que puede ser aceptado en la validación

The design of vertical formwork is dependent on the lateral pressure predicted to act on the form face. Experimental research into the construction of blocks on a gravity dam was carried out with the objective of verifying and comparing the adequacy of different theories. Pressure was measured indirectly as the load on the trusses of formwork support, which allows verification of the adequacy of the integral of the pressure envelopes, proposed by different authors, using a finite element model in ABAQUS. An analysis of the relationship between safety and exactitude was carried out with the objective of determining which method apply to formwork design depending on: safety factors, work monitoring, degree of planning and knowledge about the filling process. It was concluded by recommending the application of different theories based on these parameter values. (C) 2009 Elsevier Ltd. All rights reserved.

El diseño de los encofrados verticales depende de la predicción en la presión lateral contra la superficie del mismo. Un trabajo experimental en la construcción de 11 columnas de hormigón se ha llevado a cabo con el objetivo de verificar la adecuación de diferentes modelos. La presión ha sido medida en forma directa a partir de la colocación de sensores de presión sobre un panel del encofrado, lo que permite verificar la máxima presión lateral propuesta por los diferentes modelos. Los resultados reflejan que la predicción de los modelos coincide con la distribución hidrostática de un líquido con la misma densidad que el hormigón, lo cual es generalmente conservativo. Por lo tanto mucho más trabajo es necesario para poder realizar un modelo que sea capaz de predecir la máxima presión lateral a altas velocidades de llenado

An analysis of experimental models for predicting fresh concrete lateral pressure in columns was carried, raising the issue of a fundamental parameter like the rate of placement. Experimental data obtained from different authors were utilised for comparing the adequacy of the different theories making a division into three zones: rates of placement under 3 m/h, between 3 m/h and 10 m/h and over 10 m/h. The results were established not only in the different zones but also taking into account safety and adequacy. To determine the most suitable model according to rate of placement, level of control, vigilance, planning and inspection of the construction, eight models proposed under different standards or by different authors were compared with respect to the hydrostatic pressure produced by a liquid with concrete density. The influence of concrete yield stress, evaluated from slump test is also analyzed; the study shows a low correlation between concrete yield stress and the maximum pressure vs. hydrostatic pressure ratio. (c) 2009 Elsevier Ltd. All rights reserved.

The considerable overloads originating during the shore removal process can affect the structural safety of a multistory concrete building under construction. With an incorrect shoring removal reversal of stresses may occur which can cause concrete cracking and excessive deflections. Moreover, excessive overloads will damage the falsework, producing important economical losses due to its elevated cost. A measured program has been conducted during the shore stripping at different building levels. Results show that in general the Refined Method is adequate in a conservative form for the shore removal procedure. Then, the influence of different parameters such as concrete strength or steel reinforcement in shore removal overloads was studied. The use of the actual concrete strength and modeling the steel reinforcement produces a more accurate theoretical result. Nevertheless, these considerations do not bring major changes (less than 4%). Finally, shore overloads originating in five different shore removal procedures in a typical structure have been compared, establishing some criteria for a safe shore stripping sequence. For example the best stripping procedure found consists of removing shores by rows. (C) 2010 Elsevier Ltd. All rights reserved.