Top Six Questions about Civil Engineering
Q1) .Under what scenario shall engineers use jacking at one finish solely and from each ends in prestressing work?
During prestressing operation at one finish, resistance losses can occur and also the prestressing force decreases on the length of connective tissue till reaching the opposite finish. These resistance losses embrace the friction elicited thanks to a amendment of curvature of connective tissue duct and additionally the wobble result thanks to deviation of duct alignment from the line. Consequently, prestressing, from each ends for one span i.e. prestressing simple fraction of total tendons at one finish and also the remaining 0.5 at the opposite finish is disbursed to change an excellent distribution and to supply symmetry of prestress force on the structure.
In fact, stressing at one finish solely has the potential advantage of lower value in comparison with stressing from each ends. For multiple spans (e.g. 2 spans) with unequal span length, jacking is typically disbursed at the tip of the longer span so on offer the next prestress force at the placement of most positive moment.
Q2) What is “preset” throughout installation of bridge bearings?
“Preset” could be a technique to cut back the dimensions of higher plates of slippy bearings so as to avoid wasting the fabric value. The traditional length of a higher bearing plate ought to be composed of the subsequent components: length of bearing + two x irreversible movement + two x reversible movement. Abs initio the bearing is placed at the mid-point of the higher bearing plate while not considering the directional result of irreversible movement. However, as irreversible movement unremarkably takes place at one direction solely. The bearing is displaced/presetted a distance of (irreversible movement/2) from the mid-point of bearing during which the length of higher plate length is capable the length of bearing + irreversible movement + two x reversible movement.
Q3) In progressive launching technique of bridge construction, what area unit the measures adopted to boost ample resistance of the construction throughout the launching process?
- During the launching method the vanguard of the construction is subject to an outsized hogging moment. During this association, steel launching nose generally concerning zero.6-0.65 times span length is provided at the vanguard to cut back the cantilever moment. Sometimes, rather than victimization launching nose a tower and keep system area unit designed that serves a similar purpose.
- The construction frequently experiences various lax and hogging moments throughout progressive launching. Normally, a central prestress is provided during which the compressive stress the least bit points of bridge cross section is equal. During this means, it caters for the doable prevalence of tensile stresses in higher and lower a part of the cross section once subject to hogging and lax moment severally.
Q4) In bridge widening comes, the strategy of sewing is often used for connecting existing deck to the new deck. What area unit the issues related to this technique in terms of shrinkage of concrete?
It is a traditional follow to construct the widening a part of the bridge initially and let it keep undisturbed for many months. After that, concreting can then be disbursed for the sew between the present deck and also the new deck. During this means, the burden of the widened a part of bridge is supported by itself and hundreds arising from the new made deck won’t be transferred to the present deck that isn’t designed to require up these further hundreds.
To address this downside, the widened a part of the bridge is made a amount of your time (say 6-9 months) before handicraft to the present bridge in order that shrinkage of the new bridge can happen among this era and also the result of shrinkage stress exerted on the new bridge is decreased .
To solve this downside, speedy hardening cement is employed for the handicraft concrete therefore on shorten the time of setting of concrete. Moreover, the handicraft work is meant to be disbursed at nights of least traffic (Saturday night) and also the existing bridge could even be closed for many hours (e.g. half-dozen hours) to let the handicraft works to left undisturbed.
Sometimes, longitudinal joints area unit utilized in connecting new bridge segments to existing bridges. the most downside related to this style is that the safety concern of vehicles. The amendment of resistance coefficients of bridge and longitudinal joints once vehicles amendment traffic lanes is extremely dangerous to the vehicles. Moreover, maintenance of longitudinal joints in bridges is kind of troublesome.
Q5) What area unit the benefits of distribution the central pier and also the abutment as mounted piers?
1) For abutment pier to be assigned as mounted pier whereas the bridge is kind of long, the longitudinal hundreds thanks to earthquake area unit quite giant. Because the earthquake hundreds area unit resisted by mounted piers, the dimensions of mounted piers are giant and large. During this association, for higher aesthetic look, the choice of abutment as mounted piers might accommodate the massive size and massiveness of piers.
2) For the central pier to be designated because the mounted pier, the bridge is allowed to maneuver ranging from the central pier to the tip of the bridge. However, if the mounted pier is found at the abutment, the number of movement to be incorporated in every bearing thanks to temperature variation, shrinkage, etc. is over that once the mounted pier is found at central pier. Therefore, the dimensions of movement joints is reduced considerably.
Q6) Sometimes the facet of concrete bridges is ascertained to show black in color. What’s the rationale for this phenomenon?
In some cases, it should ensue to the buildup of dirt and dirt. However, for the bulk of such development, it’s thanks to plant or alga growth on concrete bridges. Once precipitation, the bridge surface absorbs water and retains it for a definite amount of your time. Hence, this provides a decent home ground for plant or alga to grow. Moreover, part pollution and proximity of plants offer nutrients for his or her growth. Improvement in drain details and application of painting and coating to bridges facilitate to resolve this downside. Reference is formed to Sandberg Consulting Engineers Report 18380/X/01.