A study on Strengthening of Building foundation for Storey Extension

Storey extensions are an increasingly popular way to crowded cities. Lack experience and knowledge concerning strengthening of structures are major challenges for engineers. This paper presents strengthening practice adopted for foundations of existing building when storey extension is needed. Literature concerning strengthening techniques commonly adopted and some historical cases were reviewed. A complex hall building in university of Khartoum which was rehabilitated in 2009 by strengthening the structural members of the existing building to accommodate additional floors was undertaken as a case study. The records and reports of the original design and last rehabilitation of the building were reviewed. Field inspection of the building condition before rehabilitation was carried out. The study results showed that the appropriate design, the strengthening materials used and the procedure followed are the key factors for economical and successful strengthening

Examining bias in estimating the response variable and assessing the effect of using alternative plot designs to measure predictor variables in diameter growth modeling

Diameter growth of Douglas-fir (Pseudotsuqa menziesii (Mirb.) Franco) estimated from increment cores was compared with that obtained from repeated measurements of tree diameter on permanent plots located in two Douglas-fir study areas in the central Coast Range of Oregon. Growth was measured for a 6-year period (1979- 1985). Diameter growth measured from two increment cores taken opposite to each other, provided an unbiased estimate of the stand average diameter-growth as determined from repeated measurements of diameter. However, a statistically significant trend was found in the differences in individual tree diameter-growth between the two methods of measurements. A nonlinear model was used to characterize these differences. The practical significance of the observed trend and the use of the developed model as a calibration tool, depend upon the reliability desired by the particular user. The second part was a simulation study to examine the effect upon growth model predictions of using alternative sample plot designs to measure predictor variables. Five forest stands were generated through computer simulation by use of field data and random spatial distributions. Two variable-radius plot designs and four fixed-radius circular plots were used to sample simultaneously the generated stands . Sample data then were used to simulate diameter and gross-basal-area growth in both a single-tree/distance-independent growth model and a whole-stand/diameter-free growth model. In comparing the growth predictions of each model, the plot design used to develop the model was the standard against which alternative plot designs were evaluated. Both fixed and variable area plots provide, with varying degree of precision, unbiased estimates of stand-level predictor variables. For both models, average gross basal area growth-rate predictions from 50 samples of each alternative design were not significantly different from the standard design. However, large differences in individual predictions may occur as a result of using a different plot design. The magnitude of these differences depend on the stand size and density

Effects of stand density on site index in thinned stands of Douglas-fir in the Pacific Northwest

In site index studies, the hypothesis that height growth of most conifers is independent of stand density is commonly accepted. However, some studies have shown height growth to be influenced by density particularly on medium to poor sites. In this study two locations representing a high quality site (Hoskins area, Oregon) and a relatively lower site (Rocky Brook area, Washington) were selected to examine the effect of stand density on site index in natural stands of Douglas-fir which has been repeatedly thinned at different intensities. The data for the study were obtained from the periodic measurements of the stand characteristics at the end of each thinning treatment period. The average height of the largest 40 trees per acre was used as basis for the comparison of height growth patterns among the different thinning regimes. Simple linear regression was found adequate to describe height growth of the individual plots over the age range studied (20 to 36 years at the Hoskins and 27 to 44 years at the Rocky Brook). Covariance analysis using multiple regression was used to test differences in height growth within plots under similar thinning treatments. The coefficients of the height growth equations from individual plots were used in the analysis to test for differences in height growth among the different thinning regimes. The results of the study indicated that on both sites, site index was not influenced by density over a wide range of stocking and within the age range studied

Equations for predicting the height to crown base of six tree species in the central western Willamette Valley of Oregon

This paper presents equations developed to predict the height to live crown base of six species in the central western Willamette Valley of Oregon. Weighted nonlinear regression was used to fit a separate logistic equation for each species. The predictor variables are total tree height, crown competition factor in trees with larger diameter at breast height than the subject tree, stand basal area, and diameter-height ratio. The equations will be used in two ways: 1) to estimate crown ratio on trees for which that measurement is missing, and 2) to simulate crown change in a single-tree/distance-independent growth and yield model. Application of these equations will be most reliable in stands that are free from thinning effect

International Journal of Multidisciplinary and Scientific Emerging Research The Impacts of Poor Drainage on Road Performance in Khartoum

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