Scielo RSS <![CDATA[Revista de la construcción]]> vol. 13 num. 1 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Quantification of Productivity Changes Due to Work Schedule Changes in Construction Projects</b>: <b>A Case Study</b>]]> In a copper-molybdenum open pit mine in Chile, a collective labor dispute in April 2012 halted work on the site; the main problem was the negotiation of unified work schedules for contractors, subcontractors and their own staff. To avoid conflicts that could delay this project, the parties agreed to submit to arbitration by an external agency, to determine and quantify the existence of lost productivity caused by the change of work schedules. The external agency considered three basic elements: a) the temporal dimension to allow the comparison of two work schedules, b) the acceptable range of productivity losses associated with these schedules; and c) an unbiased mechanism to allocate a productivity loss within the range associated with each schedule. This paper presents the analysis of productivity loss when work schedules are extended, the method utilized, and the results obtained. This probabilistic model randomly assigns discrete values of productivity loss for each day of the work schedules, and uses inefficiency ranges from industry research; this allows a non-biased, easy to implement, comparison of work schedules. <![CDATA[Proposal of Acceptable Air Tightness Classes for Buildings in Chile]]> In order to limit the energy demands the building ordinances establish requirements for reducing to acceptable levels the energy losses and/or gains. This situation obliges to define acceptable standards for thermal parameters. This report covered the evaluation of representative samples of Chilean homes built in 2007 and 2010 in the 54 provincial capitals of the country. A sample of 191 units was determined, representative of the construction, materials and housing architecture in Chile. Experimental techniques were used (Blower Door test) for obtaining air tightness of samples; numerical models (LBL Model) for relating the air tightness properties with the weather characteristics of every province in order to obtain infiltration coefficient classified by type of construction and province; simulation techniques (Thermal Analysis Simulation Software) for determining the energy demand of housing The Air Tightness classes are established combining two criteria: the one that measures the current state of air tightness of housings and other that limits the infiltration demand to a limit value that explains itself economically. <![CDATA[<b>Study of Atmospheric Corrosion of Reinforcement Steel in Havana, Cuba</b>]]> The atmospheric corrosion of reinforcement steel phenomenon has been frequently investigated under accelerated exposure, throughout diagnostic studies on site and no so much study under natural environmental conditions using probes with different concrete qualities. An exposure site placed at 20 m from the seashore without the presence of artificial of natural screening in the Havana northern coast was selected. Six reinforced concrete probes with water/cement ratios of 0.4, 0.5 and 0.6 and a wooden with four atmospheric pollutants devices, two of them for chloride deposition and the other two for the sulphur compounds deposition were placed in the exposure site. In each probe were placed two reinforced steel with recovering thickness of 20 and 40 mm. The increment of the atmospheric corrosion of the reinforcement steel inside in the time; permit us to estimate the service life of the structures that will be built in coastal zones of Havan a with a high level of corrosion aggressivity of the atmosphere and without the presence of any kind of artificial screening. The reinforced concrete probes with water/cement ratios of 0.5, 0.6 and 0.4 only with 2 cm of concrete coating thickness do not assure a suitable primary protection as a physic barrier, between the concrete structures. <![CDATA[<b>Prediction of the Static Modulus of Elasticity Using Four non Destructive Testing</b>]]> The static modulus of elasticity (Es) is an important parameter in the analysis of hydraulic concrete structures, changes have been made to the regulation of construction; these changes require minimum values for the Es, so now, in addition to concrete compressive strength (f'c) also Es values should be ensured. A methodology to predict Es is proposed, specifically, the Es were modeled by testing: ultrasonic pulse velocity (UPV), electrical resistivity test (ERT), resonance frequency test (RFT), the Hammer Test Rebound (HTR) and f'c. In order to generate models multiple linear regression technique was used. Cylindrical specimens were prepared in two stages, in the first stage was simulated laboratory conditions in the second stage was simulated conditions of concrete made in situ. All cylinders were subjected to non-destructive and destructive tests at different ages. The research objective is to predict Es from the results of destructive tests (traditionally employed to obtain Es) and nondestructive testing. It was possible to obtain a model whose correlation coefficient indicates the good approximation in the generated predictions.<hr/>El módulo estático de elasticidad (Es) es un parámetro importante en el análisis de las estructuras de concreto hidráulico, se han realizado cambios en la regulación de la construcción; estos cambios requieren valores mínimos de los Es, por lo que ahora, además de la resistencia a la compresión del concreto (f'c) también deben garantizarse valores de Es. Se propone una metodología para predecir Es, específicamente, los Es fueron modelados con las pruebas: velocidad de pulso ultrasónico (UPV), prueba de resistividad eléctrica (ERT), prueba de frecuencia de resonancia (RFT), prueba de rebote de martillo (HTR) y f'c. Se utilizó la técnica de regresión lineal múltiple para generar los modelos. Se elaboraron especímenes cilíndricos en dos etapas, la primera simulando condiciones de laboratorio y en la segunda simulando condiciones de concreto hecho en campo. Todos los cilindros se sometieron a pruebas no destructivas y destructivas a diferentes edades. El objetivo de la investigación es predecir Es con los resultados obtenidos de pruebas destructivas (empleadas tradicionalmente para obtener Es) y pruebas no destructivas. Fue posible obtener un modelo cuyo coeficiente de correlación indica la buena aproximación en las predicciones generadas. <![CDATA[<b>Economical-Structural Performance of Steel Moment Resisting Building Frames Using the Section Variation Technique</b>]]> Pre-engineered steel structures have become an indispensable tool in the construction industry because of their widespread use in large shopping malls, exhibition halls and industrial buildings. Such special buildings generally contain stacked materials, heavy machinery and a heavy-duty crane. Seismic loads are critical for these structures, as the location of the building changes depending on seismic activities. In this research, the performance of a typical structural steel building to be used as a shopping mall and constructed using the section variation technique is studied for all five seismic zones of Uniform Building Code 97, namely 1, 2A, 2B, 3 and 4. This study investigated the effects of the variation of the seismic forces in various seismic zones for special and ordinary steel moment-resisting building frames with response modification factor values of R=8.5 and R=4.5, respectively. The parameters studied were the economy and the structural factors, design performance and detailing of the structures. The results indicate that structural steel can be saved by up to 7% for main frames and 60-130% for the lateral bracing by using special moment-resisting building frames (R=8.5) if proper detailing/construction of the steel moment-resisting frames is carried out according to the guidelines set forth by the AISC seismic provisions.<hr/>Estructuras de acero con ingeniería previa se han convertido en una herramienta indispensable en la industria de la construcción debido a su uso generalizado en los grandes centros comerciales, salas de exposiciones y edificios industriales. Tales edificios especiales generalmente contienen materiales apilados, maquinaria pesada y una grúa de servicio pesado. Cargas sísmicas son críticos para estas estructuras, como la localización de los cambios de construcción en función de las actividades sísmicas. En esta investigación, la realización de un edificio de acero estructural, característica que se utilizará como un centro comercial y construido utilizando la técnica de la sección se estudia la variación de las cinco zonas sísmicas del Código Uniforme de Construcción 97, es decir, 1, 2A, 2B, 3 y 4. Este estudio investigó los efectos de la variación de las fuerzas sísmicas en diferentes zonas sísmicas para estructuras de edificios de acero resistentes a momentos, especial y normal, con los valores del factor de modificación de la respuesta de R = 8,5 y R = 4,5, respectivamente. Los parámetros estudiados fueron la economía y los factores estructurales, el rendimiento del diseño y el detalle de las estructuras. Los resultados indican que el acero estructural se puede ahorrar hasta un 7% para las tramas principales y 60-130% para el arriostramiento lateral mediante el uso de marcos especiales resistentes a momento de construcción (R = 8,5) si un adecuado detallado/construcción de marcos acero resistentes a momento se lleva a cabo de acuerdo con las directrices establecidas por las disposiciones sísmicas de AISC. <![CDATA[<b>Close Range Photogrammetry and Constructive Characterization of Masonry Gothic Vaults</b>]]> The representation of the plan of the roof in heritage buildings often raises the problem of direct measurement, since the points are not accessible. We currently have a wide range of indirect measurement techniques that solve this problem, and enable data to be captured on a massive scale with high levels of accuracy. The article discusses the use of Close Range Photogrammetry for the constructive analysis of gothic vaults in Tortosa Cathedral. The methodology and results of the campaign are explained below, which used technological resources that are available to any professional. The computerized processing of the 3D model generated makes possible to identify and analyze the geometric anomalies in the masonry vaults. Thereby it is obtained an unparalleled basis that enables us to undertake a detailed study of the vaulting, which was previously impossible. The geometrical deviation patterns can be related with the historical data available about the construction process of the gothic apse, fulfilling the lack of information from direct sources of some periods.<hr/>La representación del plano de la cubierta en edificios patrimoniales a menudo plantea el problema de la medida directa, puesto que los puntos no son accesibles. Actualmente disponemos de un amplio abanico de técnicas de medida indirectas que solucionan este problema y permiten la captura masiva de datos con gran precisión. El artículo presenta la utilización de la Close Range Photogrammetry para análisis constructivo de las bóvedas góticas de la Catedral de Tortosa. Se exponen la metodología y resultados de la campaña realizada utilizando medios tecnológicos al alcance de cualquier profesional. A partir del tratamiento informático del modelo 3D generado, es posible determinar y analizar las anomalías geométricas de las bóvedas de fábrica. Así, se obtiene una base documental sin precedentes que permite el estudio detallado del conjunto abovedado, antes imposible de realizar. Es posible relacionar los patrones de las desviaciones geométricas con los datos históricos disponibles sobre el proceso de construcción del ábside gótico, completando la falta de información de las fuentes directas en algunos periodos. <![CDATA[<b>Validation of the Polygon-Of-Voids Tool for Asphalt Mixtures with RAP</b>]]> Durability of an asphalt mixture is directly related to the optimum asphalt binder content, which guarantees coverage of the aggregate particles and suitable volumetric properties to ensure a good performance in service, producing an asphalt mixture that is less susceptible to aging and moisture damage. Previous research has shown that the polygon-of-voids tool, or polyvoids, is an analytical technique to determine the optimum asphalt binder content of asphalt mixtures with virgin aggregates based on the specification limits of voids, allowing a saving in time and material. However, current trends to develop new asphalt mixtures which incorporate reclaimed asphalt pavement (RAP) have created additional challenges given the nature of the design of a mixture containing aggregates with residual asphalt that make the property measurement of the bulk specific gravity of the RAP aggregate <img border=0 width=45 height=22 src="http://fbpe/img/rconst/v13n1/art07_foto2.jpg" alt="Descripción: Descripción: Descripción: http://fbpe/img/rconst/v13n1/art07_foto2.jpg">difficult. This paper aims to demonstrate the application of the polygon-of-voids tool for the design of recycled hot-mix asphalt. The results show that the method of substitution, where the value of the actual specific gravity of the RAP aggregate <img border=0 width=45 height=22 src="http://fbpe/img/rconst/v13n1/art07_foto5.jpg" alt="Descripción: Descripción: Descripción: http://fbpe/img/rconst/v13n1/art07_foto5.jpg">is assumed as the bulk specific gravity of the RAP aggregate <img border=0 width=45 height=22 src="http://fbpe/img/rconst/v13n1/art07_foto2.jpg" alt="Descripción: Descripción: Descripción: http://fbpe/img/rconst/v13n1/art07_foto2.jpg">, gives the optimum asphalt contents closest to those determined by the traditional Marshall method for the design of asphalt mixtures. <![CDATA[<b>Relationship between the Deterioration of Multi Story Buildings Facades and the Driving Rain</b>]]> In order to evaluate the behavior of facades in relation to driving rain, as well as the influence of the architectural elements in front of the deterioration, were calculated in this work the monthly directional driving rain index (dDRI-m) and the amounts of driving rain wall index (I0) to the city of Goiania, Brazil. Was performed a study of case over staining on facades through visual inspection and photographic record of buildings rendered with mortar and paint finish, with more than 12 story and construction aged 10 or under, located in the same city. Samples were collected on facades regions with stains for microbiological analyzes. As a result, it was found that facades of the same building are subject to different levels of moisture and deterioration, fact established by the correlation between the staining observed in the studies of case and the dDRI-m and I0. The stains, often described as dirt, showed the presence of microorganisms: filamentous fungi, phototrophics and actinomycetes.<hr/>Con la finalidad de evaluar el comportamiento de fachadas en relación a la lluvia dirigida, así como la influencia de los elementos arquitectónicos en la deterioración, fueron calculados en este trabajo los índices de lluvia dirigida direccional mensual (ICDd-m) y las cantidades de lluvia dirigida sobre pared vertical (I0), para la ciudad de Goiânia - Brasil. También fue realizado un estudio de caso de manchas en fachadas por medio de inspección visual y registro fotográfico de edificios recubiertos con mortero y pintura, con más de 12 pisos y con 10 o menos años de construcción, localizados en la misma ciudad. De las muestras colectadas en regiones de las fachadas con manchas, fueron realizadas análisis microbiológicos. Como resultado, se constató que las fachadas de una misma edificación están sujetas a diferentes niveles de humidad y deterioración, hecho comprobado por la correlación entre las manchas observadas en los estudios de caso y los índices ICDd-m y I0. Las manchas muchas veces descritas como suciedad, presentan microorganismos del tipo hongos filamentosos, actinomicetos y fototrofos. <![CDATA[<b>Analysis of the Optimal Sharing of Construction Risk in Public Procurement Contracts</b>]]> This paper discusses a model based on the agency theory to analyze the optimal transfer of construction risk in public works contracts. The base assumption is that of a contract between a principal (public authority) and an agent (firm), where the payment mechanism is linear and contains an incentive mechanism to enhance the effort of the agent to reduce construction costs. A theoretical model is proposed starting from a cost function with a random component and assuming that both the public authority and the firm are risk averse. The main outcome of the paper is that the optimal transfer of construction risk will be lower when the variance of errors in cost forecast, the risk aversion of the firm and the marginal cost of public funds are larger, while the optimal transfer of construction risk will grow when the variance of errors in cost monitoring and the risk aversion of the public authority are larger.<hr/>En este trabajo se elabora un modelo basado en la teoría de la agencia para analizar la transferencia óptima del riesgo de construcción en los contratos públicos de obras. El supuesto de partida consiste en un contrato entre un principal (Administración Pública) y un agente (contratista), con un sistema de remuneración basado en una fórmula de tipo lineal que incluye unos determinados parámetros que definen los incentivos para inducir el esfuerzo del contratista en la gestión de los costes. El modelo teórico se desarrolla a partir de una función de costes con un componente aleatorio, y suponiendo que tanto la Administración como el contratista presentan aversión al riesgo. Como resultados principales del trabajo cabe destacar que la transferencia óptima del riesgo de construcción al contratista será menor cuanto mayor sea la varianza de los errores de previsión de los costes de construcción, cuanto mayor sea la aversión al riesgo del contratista y cuanto mayor sea el coste marginal de los recursos públicos. Por el contrario, la transferencia óptima del riesgo de construcción será mayor cuanto mayor sea la varianza de los errores de medición de los costes y cuanto mayor sea la aversión al riesgo de la Administración.