BRICK/BLOCK Masonry c ONF E RENCE SYSTEM OF SUPERFICIAL FOUNDATION ON SOll PRESENTING POTENTIAl PROBlEMS FOR lOW-COST HOUSING CONSTRUCTED WITH STRUCTURAl MASONRY A. Márquez
ABSTRACT The widespread use in Venezuela af salid stane faundatians in develaping law-cast hausing, because it is easy ta emplay in constructian, as wel/ as the premature deteriaratian af these bui!dings due ta infrastructure and the subsail, are conducive ta making a study af the faundatian slabs, in terms af the costs structure, the processes leading ta its deterioratian and land use. This study is directed taward develaping a prefabricated campanent that wauld serve as a substratum, building a reticulate slab used as a foundation that is more salid and efficient and thus making construction easier and expanding its use where the sai! presents a possible problem.
Key words: Technalogical development in construction, progressive low-cost housing, superficial faundation, reticulate slab used as a foundaation, partial/y prefabrication, expansive soil.
The information presented here is an extract of the initial stages of the development of a technological project made by the author at the Institute of Experimentai Development in Construction (IDEC) of the Faculty of Architecture and Urbanism (FAU) of the Central University of Venezuela (UCV); therefore, the conclusions arrived at and the results obtained are empirical and partial, so that they could now be undergoing reconsideration or they could even have already been modified in accordance with calculations made and their confirmation in successive experimental stages.
"Construction of low-cost housing in Venezuela has been an urgent matter since the decade of the 7960s and lack of it has increased markedly in the past decade. According to figures obtained in the last census of 7990, approximately 60% of the country's population lives in poverty." (Hernández, B./1995) One of the thorny problems that this social drama presents is that these sectors of the population constructs its own housing, mainly in precarious conditions and without any technical criteria as regards construction, particularly regarding the soil on which the foundation is built; nevertheless, a kind of spontaneous community organization -which has its roots in the collective memory- underlies the origin and prolonged development of these "ranchos", the name popularly given in Venezuela to these dwellings that spring up almost overnight, while the illegal takeover of property is the most extensive method used as a first step in setting up the shantytowns.
"One of the principal characteristics of housing policies in developing countries is the wide gap that exists between the need for housing and the shortage of available resources to obtain sufficient financiai and budgetary leveis . ... Despite having produced much and put ali our energies into the task of management, ... we have basically always thought about the matter in quantitative terms, devoting little time considering and revising ali those aspects needed to act, 50 that we can evaluate the results, think in qualitative terms and truly occupy ourselves with the goals of our housing policy." (INAVI/1998). Th is unchanging attitude of the government has always given priority to the political interest expressed in the number of housing units built over those ethical principies that would allow public policy to be oriented toward producing integral housing wíth regard to the environment; th is fact comes to have dramatic implications since in the particular case of those in the middle- and low-income socioeconomic sectors a house has the connotation of an investment as a lifelong project. Along with th is unchanging attitude by the state entities in charge of housing policy, and regardless of the officeholders, other factors contribute to aggravate the 11 26
situation; on one hand, the plots of land set aside for official housing developments, or developments having government sponsorship, are often not entirely ideal for what is required; likewise, the cost-cutting that must be done in order to fali within the price ranges set by government norms is met only at the cost of a significant decline in building methods and materiais; affecting not only the project itself but also the process of quality-control with regard to these methods and materiais; this is further aggravated if the work done is not subjected to monitoring at reasonable time periods after the buildings are finished and handed over to the new homeowners; which leads to complete impunity on the part of the contractors and the official entities involved when the owners charge them with responsibility for the deterioration of the houses that occurs as a result of inadequate professional building methods and irresponsible practices; the owners often risk losing their investment and sometimes even risk losing their lives. Given these kinds of problems, the search for making construction methods and materiais more effective is ongoing in the area of technological development related to this branch of production, which is evidenced in diverse ways: rapidity of execution, facility of installation, less weight, durability, easy of repair, safety, less waste of material, among others; these are the challenges, singly or in combination, that researchers face. Nevertheless, except for recent innovations made with regard to the particular requirements of high-rise buildings, the field of foundations in family housing, particularly in buildings of one or two stories, seems to have been neglected for some time compared with the evident number of new alternatives in construction in other areas; these efforts have fundamentally been focused in technological developments in infrastructure that increase the efficiency of the process of erecting the structure, as well as the technical processes related to quality-control and the performance of the materiais and products used in construction. This has produced, given the unvarying methods used in construction activity, an apparent lack of significant advances in developing new ideas concerning foundations as such, so as to contribute to reducing the amount of material used and decreasing the number of processes employed in producing them; particularly with regard to the layers used in constructing foundations, which, because of their special shape and portable nature, require proportionally a greater quantity of concrete and steel used to reinforce their structure. This situation is particularly important with regard to low-cost housing, beca use this kind of infrastructure has been widely employed in its solid-structure form in construction, despite the fact that it does not have the most efficient relation of mass to resistance; so that it is easier to produce it compared with the kind used in isolated cases in buildings of modest size; especially in the case of groups of houses, where several housing units in the group make use of a single foundation layer, which has several comparative advantages with regard to technical and economic performance of the construction; likewise, in he case of those houses that have a superstructure of portative walls, which need this kind of cement works for stability. 7727
1. Geagraphic distributian af expansive c/ays in Venezuela.
GEOGRAPHIC DISTRIBUTION OF EXPANSIVE CLA YS IN VENEZUELA 2. Geagraphic distributian af seismic faults in Venezuela.
GEOGRAPHIC DISTRIBUTION OF SEISMIC FAULTS IN VENEZUELA
50 there is an area of research to be undertaken in foundation layers for housing for low-income groups, both with regard to their contribution to the economics of cost structures and to their potential as a mechanism in preventing the deterioration produced in the different components of the structures as a result of excessive interaction with strata of the subsoil; also, as a factor in safer use of land that possesses unsafe characteristics. In Venezuela, almost 50% of the states in its territory contain areas made up of retro-expansive soil, which almost totally coincide with the areas of highest population density and seismic activity: the north-central coastal region and the Andes. This reality allows us to assess the importance of dealing with the different areas of construction regarding it, both in connection with the infrastructure of services and with the buildings themselves. 71 28
3. SPEClFIC AIMS This technological development project has as its conceptual guide the Program to Promote Innovation in Production and Commercialization of Materiais and Components in Low-cost Housing (PRO-MAT) (Hernández, H. / 1989), which aims to reduce housing construction costs through technological development in materiais and components. This is based in particular on the following priorities established in the PRO-MAT project: • The criticai problems affecting the structural stability of the houses. • The effect that materiais and techniques have on construction costs and quality. Based on the foregoing, this project has these fundamental goals.
Reduce the amount of concrete prepared for making foundation layers as an alternative technique for modern low-cost housing of up to two stories high, taking into account those extreme circumstances when the structure is to be built on retro-expansive soil.
Streamline the process of producing foundation layers by considering the use of prefabricated housing, an accepted and efficient method used in construction, which would simplify the building process while giving greater support to the whole infrastructure, resulting in better structural performance and in a saving when steel reinforcement is taken into account.
Contribute to the production and spreading of knowhow in technological development in construction, particularly about the superficial foundations.
4. PRELlMINARY PROPOSALS On the basis of conclusions that were drawn from the foregoing analysis and from research conducted on state-of-the-art in housing, some proposals were made to serve as preliminary guidelines with regard to technological development. • To study the different types of foundation layers: direct, branched, bidirectional, regular, rigid, with regard to supporting a fixed weight and absorbing a dynamic force, to determine efficiency in relation of mass to resistance . • To limit the study of structural performance of foundation layers to houses of up to two stories high, constructed with structural masonry, with usual residential span and is built on a surface characterized by minor movement of the soil or retro-expansion . 7729
• To study reducing the amount of material used to produce the prefabricated component and the foundation layer, as well as taking into account the design, so that it contributes not only to determining the areas in which the lines of resistance are to be found, thus stream lining construction, but also to make it a structura l support for the component that is already built, lending integral solid ity to the unit; research will be carried out on the geometric aspect of the layer and on the surface in terms of resistance and stress forces. • To study the production process of the prefabricated component, both in industrial factories and self-construction . • To link as much as possible the construction of foundation layers with the idea of progressive housing.
5. PROPOSAL FOR TECHNOLOGICAL DEVELOPMENT "At times one ca/ls structural design the work that only deals with determining stress forces, thickness of steel plotes or sections made of concrete, or similar activity. PeopIe forget that structural design is a creative process aimed at searching for and discovering the structural forms that meet the basic criteria of the project in an adequate manner. ... The number of structural calculations become ever greater while interest in the design of the structure itself diminishes. " (Zalewski, W./1987)
5.1. Analysis of geometric module Given that the aim of the study deals w ith a prefabricated component that will allow it to be built on the substratum, in constructing a foundation layer or plate, with the above-mentioned characteristics; it was considered opportune to take into account the geometric properties of regular design, both in individual units and in units grouped together. To this end, the geometric properties of the units were analyzed: square, triangular and various polygonal designs; the first of these was chosen beca use it possesses severa I comparative advantages as regards construction on a square surface; these are the most usual in projects for low-cost housing.
3. Horizontal grouping pattern.
'" I'", ',,-
HORIZONTAL GROUPING PATIERN
5.2. Geometric-structural analysis "The conclusions drawn from the observations and considerations made on the transmission of forces through the structure lead one to consider the flow of internaI forces . ... Once the principIes of how these forces work is known, one can assume an active role by seeking to channel of the flow of internaI forces through the shape of the structural geometry and the materiaIs used." (Zalewski, W./op. cit.)
Given the choice of using a square horizontal surface for the housing unit, an analysis was made of the basic transmission of the flow of internai forces as an element in a three-dimensional projection (cube) and submitted to an axial vertical weight; then a similar analysis was made of the reticular form of housing units grouped together.
5.2.1. Performance of single units or grouped units For each force applied in axial form to a virtual prism of the group, a typical diagram of the flow of forces repeated n times will be generated.
5 .2.2. Diagram of positive-negative flow of internaI forces In the case of a continuous and uniform layer, the diagram overlaps n times . In the case of a reticular section, the diagram is the reverse and will be repeated for each section of the surface on which stands a unit of branched foundation.
4 . Individual and group behavior.
INDIVIDUAL ANO GROUP BEHAVIOUR
5 . Diagram of the f10w of internaI forces in solid slab.
OIAGRAM OF THE FLOW OF INTERNAL FORCES IN SOLlO SLAB 6. Diagram of the f10w of internaI forces in the reticular slab.
DIAGRAM OF THE FLOW OF INTERNAL FORCES IN RETICULAR SLAB
5.2.3. Performance with regard to retro-expansive soils "There are different ways to control expansion. One of them is to construct the building 's cement structure containing cavities, so that the soi! expands freely inside them, without affecting the structure . .. . In this way, the expansion can be directed in the direction one wants." (Fratelli, M ./1993).
5.3. Summary of the requirements of the proposaal Prefabricated plate w ith a square base for housing unit, to build foundation layer: direct, branched, bidirectional, regu lar, rigid, to support fixed weights and absorb dynamic forces, including retro-expansive ones. Light element easily handled whose geometry contributes to reducing the use of materiais in the consolidation of the structura l un it (concrete and steel), as well as in its production . Structural support element through experimenting with the geometry in threedimensional form, which wou ld cont ribute to the channeling of the flow of interna i forces; based on the negative of the diagram of the flow of the typica l section of the bidirectional grid . Element that allows the controls of expansion of the soi l, performed through a geometry in alveolar shape. 11 32
7. Guiding the expansion of the soi/.
GUIDING THE EXPANSION OF THE SOIL
8. Cy/indrica/ surfaces.
Element confined to its own form the lower edge of the branched shape, controlling the amount of concrete used.
5.4. Geometric-tridimensional definition Of the three-dimensional geometric shapes, the most efficient (in terms of the relation of mass to resistance) with regard to the effect produced by stress forces, channeling the flow of internai forces with minimal effect in the support structure; one finds those derived of cylindrical surfaces and also those generated by turning (spherical, conical and others), like those produced by the intersection of curved sections or the movement of lines in a certain direction (translational, synclastical, anticlastical and others). Of the requirements of the proposal with the properties of cylindrical surfaces, a preliminary geometry of the unit is made, which could be summarized as that of a synclastic square-based surface. 113
5.5. Study of alternatives 9. Ana/ysis af a/ternatives.
SutI*J& _ _
i'l,~r, 7, '\~ AfJ?i1' + j~ !'I r:~ /'tff j
1 . 1 r::~2
Li------___________________- L_____ _ _ _ _ _ _ _ _ _-.-J ANALYSIS OF ALTERNATIVES
6. CONClUSIONS After evaluating the alternatives, the following conclusions were reached: 134
6.1. Pre-measurements Based on the dimensional ratios of structural openings and spatial proportions that usually appear in low-cost housing proposals; the two-dimensional module of 0.80 x 0.80 was chosen for the preliminary design proposal; the measurement to be used to perfect the vertical profile of the three-dimensional element, based on geometric-resistant relations of the shape.
Geometric-resistant grounds Bearing in mind that that the vertical sections of the element correspond to the geometric profile and the behavior of a bow contained in the section plan, the following precisions are made: "The thrust of o bow is inversely proportionol to its orrow. To reduce the thrust, the orrow of the bow should be os big os possible." (Engel, H./1977)
The magnitude of the horizontal reactions at the lower ends of the arches is estimated for half of the vertical section, according to the following ratios:
Preliminary measurement Based on the two-dimensional module of 0.80 x 0.80 and an arrow relation in its middle section of 1/3 of the opening, the element's profile is as follows:
10. Horizontal reactions in bows .
---- - 113 apan
HorizonIaI ntedlon 1
HORIZONTAL REACllONS IN ARCHES
11. Preliminary dimensions.
-p.'0 I r-
~Lt±lH+tl+tff-tktT rJiZf:iill PRELlMINARY DIMENSIONS (mt.)
Horizontal Grouping Pattem.
12. Preliminary dimensions.
PRELlMINARY DIMENSIONS (ml)
13. Horizontal grouping pattern.
HORIZONTAL GROUPING PATIERN
14. Reticular slab.
6.2. Materiais As a first estimate, the materiais to be studied are: high resistance concrete only with fine aggregate, fiber-cement and ferro-cement.
The author thanks the following institutions for their financiai support which made it possible to present this paper at 12th INTERNATIONAL BRICK/BLOCK MASONRY CONFERENCE. Madrid, Spain. June 2000. Consejo de Desarrollo Científico y Humanístico de la Universidad Central de Venezuela. CDCH-UCV (Scientific and Humanist Development Council, Central University of Venezuela). Comisión Nacional de Investigaciones Científicas y Tecnológicas. CONIClT (National Scientific and Technological Research Commission). Asociación de Profesores de la Universidad Central de Venezuela. APUCV (Professors' Association, Central University of Venezuela)
BIBlIOGRAPHIC REFERENCES ENGEL, Heinrich. Sistemas de Estructuras. Blume Ediciones. Madrid. 1977. Pg. 62. FRATELlI, María G. Suelos, Fundaciones y Muros. Bonalde Editores. Caracas. 1993. Pg. 61. HERNÁNDEZ, Beatriz. Innovación Tecnológica para Viviendas de Construcción Progresiva en Venezuela. Mimeograph. IDEC, FAU, UCV. Caracas. Venezuela. 1995 . Pg. 2. HERNÁNDEZ, Henrique. Programa de incentivos a la innovación en la producción y comercial ización de materiales y componentes para el hábitat popular (PRO-MAT). Revista Tecnología y Construcción N° 2. Caracas. 1986. Pg. 35. INAVI. Arq. Urb. Pedro Sosa Franco with 60 years of experience in low-cost urban developments in Venezuela. EYKON c.A. . Caracas. 1988. Pg. 7. ZALEWSKI, Waclaw. Cálculo versus diseno. Revista Tecnología y Construcción N° 3. Caracas. 1987. Pg . 103.
GRAPHIC REFERENCES LA MARCA, Gabriel et aI. Fundaciones directas sobre arcillas expansivas. Mimeograph . Faculty of Engineering. UCV. Caracas. 1986. FUNVISIS . Falias geológicas en Venezuela . Fundación Venezolana de Investigaciones Sísmológicas o Mimeograph. 1987. ENGEL, Heinrich. Sistemas de Estructuras. Editorial Blume. Madrid . 1° Edición en espaneI. 1970. 1° Reimpresión. 1977. 11 3i
MARQUEZ, A. Desarrollo de sistema de fundación superficial para suelos potencialmente problemáticos, como una opción para la vivienda de bajo costo. Mimeo. IDEC-FAU-UCV. 1999. FRATELLI, María G. Suelos, Fundaciones y Muros. Bonalde. Editores. 1° Edición. Caracas. 1993. OWEN, Roy. Cubiertas. Editorial Blume. Barcelona. 1° Spanish edition. 1978.
REFERENCE BIBlIOGRAPHY ALEMO. 111 Encuentro Nacional de la Vivienda. Summary. Fundación Polar - ALEMO. Caracas.1995 . ALEMO. IV Encuentro Nacional de la Vivienda. Summary. LUZ - ALEMO. Caracas.1997 . ANPAE. li Progetto. Problemi e soluzioni per I'edilizia. Associazione Nazionale Produttori di ArgilIe Espanse. Milano. CAZAR, Pfander. Sugerencias para prevenir la fal ia de estructuras. fundadas sobre suei os expansivos. Mimeograph. Faculty of Engineering . UCV. Caracas. 1973. CILENTO, Alfredo. Anotaciones sobre el proyecto de ley de política habitacional. Revista Tecnología y Construcción N°3. IDEC.FAU. UCV. Caracas. 1987. ClLENTO, Alfredo. Sincretismo e Innovación Tecnológica . Revista Tecnología y Construcción N° 12. IDEC. FAU. UCV. Caracas. 1996. CILENTO, Alfredo et aI. Programa Experimental de Gestión Habitacional Local (PEGHAL). Revista Tecnología y Construcción N° 13-1. IDEC. FAU. UCV. Caracas. 1997. ClLENTO, Alfredo . Tendencias tecnológicas en la producción de viviendas. Revista INTERCIENCIA. Vol. 23 N° 1. Caracas. 1998. COLOCA. Proyecto Vivienda Tipo Lock joint. Mimeograph. Caracas.1979 . COVENIN. Norma 1756-98. Edificaciones Sismorresistentes. FONDONORMA. FUNVISIS. MINDUR. Caracas. 1998. ENGEL, Heinrich. Sistemas de Estructuras. Editorial Blume. Madrid. 1° Spanish edition. 1970. 1° Reimpresión . 1977. FERREIRA, José M . Disenos típicos de placas fundaciones. Mimeograph. Faculty of Engineering. UCV. Caracas. 1984. FRATELLI, María G. Suelos, Fundaciones y Muros. Bonalde. Editores. l ° Edición . Caracas. 1993. GONZÁLEZ, Rafael et aI. Métodos comparativos de análisis y diseno de placas fundación tomando en consideración la rigidez dei suelo. Mimeograph . Faculty of Engineering. UCV. Caracas.1987. HERNÁNDEZ, Beatriz. Innovación tecnológica para viviendas de construcción progresiva en Venezuela . Mimeograph . IDEC. FAU. UCV. Caracas. 1995. HERNÁNDEZ, Beatriz. La vivienda de bajo costo. Mimeograph. IDEC. FAU. UCV. Caracas. 1996. HERNÁNDEZ, Henrique. Programa de incentivos a la innovación en la producción y comercialización de materiales y componentes para el hábitat popular (PRO-MAT). Revista Tecnología y Construcción N° 2. IDEC. FAU . UCV. Caracas. 1986. HERNÁNDEZ, juan. La casa de un solo muro. Editorial Nerea. 1° Edición. Madrid. 1990. HODGKINSON, Allan y otros.Estructuras. Editorial Blume. Madrid. 1° Spanish edition . 1976. 11 38
INAVI. 60 anos de experiencias en desarrollos urbanísticos de bajo costo en Venezuela. E?KON c.a. 1 0 Edición. Caracas. 1988. LA MARCA, Gabriel y otros. Fundaciones directas sobre arcillas expansivas. Mimeograph. Faculty of Engineering. UCV. Caracas. 1986. LAQUIÁN, Aprodicio. Vivienda básica . Centro Internacional de Investigaciones para el Desarrollo (ClIO). Colombia. 1985 . LATINA, Corrado. Muratura portante in laterizio. Edizioni Laterconsult. Roma. 1994. LOVERA, Alberto y otra . Oiseno y evaluación económico-financiero para proyectos de urbanizaciones dei hábitat popular. UCV. Caracas. 1991. LLORENS, Joseph I. y otro. Construcció amb bloc de formigó. Edicions tectes. Barcelona. 1997.
MARRERO, Mercedes. La mampostería estructural de bloques de concreto. Tercera Parte. Mimeograph. 10EC. FAU. UCV. Caracas. 1991. MÁRQUEZ, Antonio et aI. Análisis y disefio de fundaciones directas mediante microcomputadoraso Mimeograph . Faculty of Engineering . UCV. Caracas.1987. OLlVARES, Alberto. Tablas para losas continuas y muros de concreto armado. Fundaciones. Litográficas Federal. Caracas. 20 Edición. 1972. OLlVERI, Mario. Prefabricación o metaproyecto constructivo. Editorial Gustavo Gili. Barcelona. 10 Spanish edition . 1972. OWEN, Roy. Cubiertas. Editorial Blume. Barcelona. 10 Spanish edition. 1978. PÁEZ, Cruzbert y otro . Comportamiento de tipos de fundaciones directas sobre arcillas expansivas y consideraciones de disefio. Mimeograph. Faculty of Engineering. UCV. Caracas. 1987. PÉREZ, Pedro A. Patología de las fundaciones superficiales. Mimeograph. Faculty of Engineering.UCV. Caracas.1992. RICO, Alfonso et aI. La Ingeniería de Suelos en las Vías Terrestres. Carreteras, Ferrocarriles y Aeropistas . Volumen I y 11. Editorial Limusa . México. 50 Edición. 1984. SAFINA, Salvador. Oesarrollo de un modelo para la interacción losa de fundación-suelo. Mimeograoh. Faculty of Engineering. UCV. Caracas. 1987. SALVADORI, Mario y otro. Estructuras para Arquitectos. Ediciones La Isla. Buenos Aires. 50 Edición . 1978. SALVATIERRA, Miguel. Arquitectura para la reducción de danos por terremotos en edificaciones esenciales urbanas. Mimeograph . ULA. FAA. Mérida. 1995. TECNIDEC s.a. Informe Final dei Programa de Promoción Industrial. Mimeograph. Caracas. 1986. TIMOSHENKO, S. Resistencia de Materiales. Editorial Espasa Calpe. Madrid. 10 Spanish edition . 1957. ZALEWSKI, Waclaw. Cálculo versus Diseno. Revista Tecnología y Construcción N° 3. Caracas. 10EC. FAU . UCV.1987.