Department of Structural and Construction Engineering

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    Behavior of Wood in Transverse Compression
    (1994) Pellicane, P. J.; Bodig, Jozsef; Mrema, Alex L.
    A finite element analysis program exists to evaluate the stress distribution in wood members subjected to perpendicular-to-grain (transverse) compression. In this study, the program was used to perform parameter studies to evaluate the effects of key variables on the distribution of stresses and the maximum stress concentrations in wood subjected to transverse compression. These variables included: specimen geometry (length/depth), loading geometry (loaded length/specimen length), and material properties (ratio of moduli of elasticity of the wood in the direction of loading/perpendicular to loading). The results showed that a complex state of stress exists in members even when the load is distributed over the entire specimen surface. In particular, numerically-determined stresses nearly 3.5 times the nominal stress were found for certain combinations of input parameters. In addition, an empirically-derived equation is presented that estimates the magnitude of maximum stress concentration as a function of the three parameters investigated. The equation was developed with the use of multiple regression techniques and had a correlation coefficient of 0.958.
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    Modeling Wood in Transverse Compression
    (1994) Pellicane, P. J.; Bodig, Jozsef; Mrema, Alex L.
    A plane-stress, finite element model has been developed to predict the stress distribution in wood members subject to perpendicular-to-grain compression. This model exploits linear-strain, isoparametric triangular elements used in sufficient number to achieve a convergent solution. Model verification was achieved through comparison of numerically obtained deformation predictions with corresponding experimental data obtained from actual test specimens. Twenty-seven specimens were instrumented to determine their deformations at numerous locations. Test materials were sampled from three logs (two engelmann spruce, one western hemlock). Specimens were fabricated with three widely different orthotropic ratios, three geometries (length/depth ratios), and three loading geometries (uniformly distributed load across the entire length, one-half length, and one-quarter length). In total, 377 experimental measurements on 27 specimens were compared to finite element predictions. The results showed that on average the model predicted local deformation to within 5%.
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    Importance of Planned Maintenance Systems for Buildings
    (1997) Rubaratuka, Ignas A.
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    Load Test for the Fire Gutted Nasaco Building
    (1997) Rubaratuka, Ignas A.; Mpinzire, S.; Makunza, J. K.
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    Numerical Investigation of Bifurcation of Steady Oscillations in Shallow Plates
    (1998) Rubaratuka, Ignas A.; Isakhanov, G. V.
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    Earth Building in Tanzania – Use of Soil Stabilized Bricks and Blocks
    (2005-06) Mrema, Alex L.
    This paper presents experimental results of investigations done on the use of stabilized earth (soil) for the manufacture of bricks and blocks. The soil used was clayey sand of low plasticity. Two types of stabilizers were used to make stabilized bricks and these were cement and a combination of cement and lime. Different stabilizer proportions were employed. Results of tests carried on these bricks at 28 days indicate an optimum mix proportion of 7% cement if cement is used alone and an optimum mix proportion of 5% each if a combination of lime and cement is used as a stabilizer. With these stabilizer contents we obtain bricks of strengths of at least 2.5N/mm2 with acceptable functional capabilities in a wall for low cost housing. To make bricks comparable in strength with those made of cement and sand with a minimum strength of at least 3.5N/mm2 for load bearing walls as suggested in the Tanzania Standard, TZS 283:1986, the optimum mix proportion was found to be 8.5% cement and 7% each if cement and lime is used in combination. It is suggested that further research on the effectiveness of the various other stabilizers like bitumen, gypsum, ash/sand, and cow dung is required for the different types of soils commonly found in Tanzania.
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    Cement Bonded Wood Wool Boards from Podocarpus Spp. For Low Cost Housing
    (2006) Mrema, Alex L.
    This paper gives results of a preliminary study on the properties of cement bonded woodwool boards manufactured as composites by using wood wool (excelsior) from podocarpus spp. wood species and ordinary Portland cement. Two main parameters were varied during the investigation and these were the width of the wood wool and the cement to wood wool ratio. Results show that the optimum mix proportion is three parts of cement to two parts of wood wool by weight and that a smaller excelsior width gives higher board strengths. The results from tests on flexural strength, compressive strength and tensile strength far exceeded the requirements of the German Standard DIN 1101:1989. Results of water absorption and swelling were, however, higher than those specified in the standard but this was attributed to insufficient pressure on the boards during manufacture an anomaly which can be corrected. The potential uses of the boards are in basements, floor units, permanent shuttering, partitioning, sound insulation in walls, ceilings and floors, roofs, sound barriers and thermal insulation. Further research is required to investigate the use of different wood species and different mineral binders.
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    Management of Pavement Network Maintenance and Rehabilitation Planning Using Shuffled Complex Evolution
    (2007) Mturi, Matiko S.; Shibayama, Tomoya
    This paper presents an approach for optimization of segment-linked maintenance and rehabilitation plan for a pavement network by using shuffled complex evolution. It extends the works of Nunuo and Agyei (2000) by improving the exploration-exploitation balance of the algorithm and by using a realistic pavement deterioration model to solve the problem of multiple maintenance and rehabilitation activities. An example to maximize the serviceability of the road network under a fixed budget and minimum serviceability level policy is also presented. The result of the optimization process using a part of Kanagawa prefecture road network showed very good results with reasonable computational times.
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    Assessment of Strength Compliance with Standards for Tanzania Eucalyptus Wood Poles Treated with Copper-Chromium-Arsenic Compounds
    (2007-07) Mrema, Alex L.
    Samples of copper-chromium arsenic compounds (CCA) treated Eucalyptus poles for power transmission were sampled from a lot following Militmy Standard MlL-STD 105D, Single sampling, Tightened Inspection, Acceptable Quality Level (A QL) of 4 as provided for in the South African Standard SABS 754: 1994 from lots containing 151-500 poles. Samples were randomly selected from a lot. Maximum fiber stresses were evaluated taking into account the actual taper in each pole. The cantilever loading test was peiformed on the samples following SABS 754:1994. It was found out that the average taper for the poles was smaller than that assumed in the standard due to the dijJerent pole growth characteristics and environment in Tanzania and that the average modulus of elasticity obtained for the poles was lower than the average assumed in SABS 754: 1994. The poles also showed excessive deflections at working loads. It is recommended to the Tanzania Bureau of Standards that although SABS 754: 1994 ;s meant to be used for eucalyptus poles grown ill Southern Africa south of the Sahara that are treated with creosote or CCA there is a need to review it to take into aCCOl/nt the actual characteristics of the poles grown in Tanzania where they are normally grown in highland areas with higher rainfall and colder climates.
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    Proposal of Simple Pavement Deterioration Model by Using In-Service Survey Data
    (2007-07) Mturi, Matiko S.; Shibayama, Tomoya
    In this paper a nonlinear deterministic flexible pavement performance model is presented. The model uses the maintenance control index calculated from in-service condition survey data as its independent variable, and pavement characteristics of initial condition, structure and traffic loading as its dependent or explanatory variables. The parameters of the model are estimated using Kanagawa Prefecture Road Network condition survey data. The results of the model show that the model reproduces correctly the actual in-service pavement deterioration trend. This model is simple in its expression, uses a simple estimation method, and uses readily available data, consequently reducing the cost of model estimation. It therefore, suggests a promising avenue for improving the pavement performance prediction and consequently the pavement management system.
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    Pavement Rehabilitation Management: Performance Modeling and Rehabilitation Programming
    (2007-09) Mturi, Matiko S.
    Damage to the pavement begins from the first day of utilization; thus, timely and suitable maintenance rehabilitation are required to prevent substantial pavement damage and premature loss. Pavement management systems are used to developing efficient policies to monitor, maintain and rehabilitate deteriorating pavements. These systems consist of pavement inventory and condition information, pavement performance models, and pavement maintenanca and rehabilitation optimal programmes. This paper develops a pavement performance model, and the maintenance and rehabilitation optimal programme at a network level. The performance model is a non-linear empirical whose parameters are estimated from in-service pavement data. The shuffled complex evolution method is used to develop the optimum programming of the maintenance and rehabilitation at a network level. In both cases, the Kanagawa prefecture road network inventory and condition survey data were used.
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    Quality Control in the Construction of Reinforced Concrete Buildings in Dar es Salaam
    (2008) Rubaratuka, Ignas A.
    Quality Control in the construction industry is very important to ensure that what is being done conforms to the applicable standards or good practice and the contract documents. In this article, results of investigations conducted at different construction sites for reinforced concrete buildings in Dar es Salaam to check if quality control measures are being implemented are discussed. It has been established that generally quality control is not properly carried out. Finally, measures to enhance quality control on sites are outlined.
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    Application of Non-Destructive Testing in Evaluating Reinforced Concrete Structural Elements in Buildings
    (2008) Rubaratuka, Ignas A.; Ndumbaro, P.
    Of recent a large nllmber of existing rei"forced concrete bllildings have reqllired reconstruction, renovation and improvement. This tendency poses a "w"ber of problellls that have to be solved, the main aile being to determine the actual strength condition of the structural components/elements of the bllilding. It includes determ inatioll of the quality of materials used, specificatiol/ orthe types (/I/d description of apparent fa II Its and damages and extent of wear of the bllilding. To undertake this evaluation, non - destructive testing methods are IIsed. In this paper, applications of lion - destructive testing methods to determine the strength state of reinforced concrete colllll1ns with corbels and to establish their structural strength so as to deterl7line the capacity of a mobile crane to be installed is olltlined.