For many years bridges had been designed as a series of simple spans with a corresponding number of expansion joints. Without the help of modern computers and calculators, designers often found the analysis of continuous-span bridges to be a tedious task. Therefore, designers sometimes adopted a simpler approach of designing multiple simple-span bridges. Although bridge expansion joints relieve secondary stresses of the superstructure from thermal and moisture changes of the deck, this solution caused more problems than it solved! Expansion joints cause structural deterioration problems because of:
- Leakage of road salt runoff onto the superstructure and substructure
- Corrosion and deterioration of beams, bearings and bridge seats under the joints
- Need to maintain and periodically replace the joints
Construction estimating is essentially a calculation of the expenses that will be incurred while doing various items of work. When you get a total of the probably expenses, you will then have an estimated cost of the work that is to be done. Construction estimating in building should be a very close approximation of what the project is going to actually cost. Whether or not the estimate actually agrees with the actual cost will depend upon the job that the contractor did when estimating building construction costs.
The preparation of estimates represents one of the most important functions performed in any business enterprise. In the construction industry, the quality of performance of this function is paramount to the success of the parties engaged in the overall management of capital expenditures for construction projects. The estimating process, in some form, is used as soon as the idea for a project is conceived. Estimates are prepared and updated continually as the project scope and definition develops and, in many cases, throughout construction of the project or facility.
The parties engaged in delivering the project continually ask themselves “What will it cost?” To answer this question, some type of estimate must be developed. Obviously, the precise answer to this question cannot be determined until the project is completed. Posing this type of question elicits a finite answer from the estimator. This answer, or estimate, represents only an approximation or expected value for the cost. The eventual accuracy of this approximation depends on how closely the actual conditions and specific details of the project match the expectations of the estimator. Extreme care must be exercised by the estimator in the preparation of the estimate to subjectively weigh the potential variations in future conditions. The estimate should convey an assessment of the accuracy and risks.
A landslide is a general term for a wide variety of downslope movements of earth materials that result in the perceptible downward and outward movement of soil, rock, and vegetation under the influence of gravity. The materials may move by falling, toppling, sliding, spreading, or flowing. Some landslides are rapid, occurring in seconds, whereas others may take hours, weeks, or even longer to develop.
Many factors contribute to slides, including geology, gravity, weather, groundwater, wave action, and human actions. Although landslides usually occur on steep slopes, they also can occur in areas of low relief. Landslides can occur as ground failure of river bluffs, cut and-fill failures that may accompany highway and building excavations, collapse of mine-waste piles, and slope failures associated with quarries and open-pit mines. Underwater landslides usually involve areas of low relief and small slope gradients in lakes and reservoirs or in offshore marine settings. Typically, a landslide occurs when several of these factors converge.