A typical bolted connection with washer
👇👇👇👇👇👇👇👇👇
@civil_engineers_team

Various washers used in general practice
👇👇👇👇👇👇👇👇👇
@civil_engineers_team

#general @civil_engineers_team

8.What is the difference between normal bolts and high friction grip bolts?

High friction grip bolts are commonly used in structural steelwork. They normally consist of high tensile strength bolts and nuts with washers. The bolts are tightened to a shank tension so that the transverse load across the joint is resisted by the friction between the plated rather than the bolt shank’s shear strength.

@evolvingcivilengineers

Load transmission by high friction grip bolts
👇👇👇👇👇👇👇👇
@civil_engineers_team

#roadworks @civil_engineers_team

Does the use of concrete road enhance fuel saving when
compared with bituminous road?

Concrete road belongs to rigid pavement and they do not deflect under traffic loads. On the contrary, bituminous pavement deflects when subjected to vehicular load. As such, for concrete road no extra effort is paid on getting out of deflected ruts which is commonly encountered
for bituminous pavement. Hence, vehicles using concrete road use less energy and there is about 15-20% less fuel consumed when using concrete road when compared with bituminous road.

👇👇👇👇👇👇👇👇👇👇👇👇
@civil_engineers_team

#bridgeworks @civil_engineers_team

Question: Under what situation shall engineers use jacking at one end only and from both ends in prestressing work?

During prestressing operation at one end, frictional losses will occur and the prestressing force decreases along the length of tendon until reaching the other end. These frictional
losses include the friction induced due to a change of curvature of tendon duct and also the wobble effect due to deviation of duct alignment from the centerline. Therefore, the prestress force in the mid-span or at the other end will be greatly reduced in case the
frictional loss is high.
Consequently, prestressing, from both ends for a single span i.e. prestressing one-half of total tendons at one end and the remaining half at the other end is carried out to enable a even distribution and to provide symmetry of prestress force along the structure.
In fact, stressing at one end only has the potential advantage of lower cost when compared with stressing from both ends. For multiple spans (e.g. two spans) with unequal span length, jacking is usually carried out at the end of the longer span so as to provide a higher prestress force at the location of maximum positive moment. On the contrary, jacking from the end of the shorter span would be conducted if the negative moment at the intermediate
support controls the prestress force.

However, if the total span length is sufficiently long,
jacking from both ends should be considered.

@civil_engineers_team

Prestressing
@civil_engineers_team

#bridgeworks @civil_engineers_team

Question: What is “preset” during installation of bridge bearings?

“Preset” is a method to reduce the size of upper plates of sliding bearings in order to save the material cost. The normal length of a upper bearing plate should be composed of the following components: length of bearing + 2 x irreversible movement + 2 x reversible movement. Initially the bearing is placed at the mid-point of the upper bearing plate without considering the directional effect of irreversible movement. However, as
irreversible movement normally takes place at one direction only, the bearing is displaced/presetted a distance of (irreversible movement/2) from the mid-point of bearing
in which the length of upper plate length is equal to the length of bearing + irreversible
movement + 2 x reversible movement. In this arrangement, the size of upper plate is
minimized in which irreversible movement takes place in one direction only and there is no
need to include the component of two irreversible movements in the upper plate.


Note: “Preset” refers to the displacement of a certain distance of sliding bearings with respect to upper
bearing plates during installation of bearings.

👇👇👇👇👇👇👇👇👇
@civil_engineers_team

#bridgeworks @civil_engineers_team

Question: In incremental launching method of bridge construction, what are the measures adopted to enhance sufficient resistance of the superstructure during the launching process?


(i) During the launching process the leading edge of the superstructure is subject to a large hogging moment. In this connection, steel launching nose typically about 0.6-0.65
times span length is provided at the leading edge to reduce the cantilever moment.
Sometimes, instead of using launching nose a tower and stay system are designed
which serves the same purpose.

(ii) The superstructure continually experiences alternative sagging and hogging moments during incremental launching. Normally, a central prestress is provided in which the compressive stress at all points of bridge cross section is equal. In this way, it caters for the possible occurrence of tensile stresses in upper and lower part of the cross section
when subject to hogging and sagging moment respectively. Later when the whole
superstructure is completely launched, continuity prestressing is performed in which the location and design of continuity tendons are based on the bending moments in final completed bridge condition and its provision is supplementary to the central prestress.


(iii)For very long span bridge, temporary piers are provided to limit the cantilever moment.

👇👇👇👇👇👇👇👇👇
@civil_engineers_team

Incremental launching of bridge
@civil_engineers_team

#bridgeworks @civil_engineers_team

Question: In bridge widening projects, the method of stitching is normally employed for connecting existing deck to the new deck. What are the problems associated with this
method in terms of shrinkage of concrete?

In the method of stitching, it is a normal practice to construct the widening part of the
bridge at first and let it stay undisturbed for several months. After that, concreting will then
be carried out for the stitch between the existing deck and the new deck. In this way, the
dead load of the widened part of bridge is supported by itself and loads arising from the
newly constructed deck will not be transferred to the existing deck which is not designed to
take up these extra loads.
One of the main concerns is the effect of stress induced by shrinkage of newly widened
part of the bridge on the existing bridge. To address this problem, the widened part of the bridge is constructed a period of time (say 6-9 months) prior to stitching to the existing bridge so that shrinkage of the new bridge will take place within this period and the effect of shrinkage stress exerted on the new bridge is minimized.
Traffic vibration on the existing bridge causes adverse effect to the freshly placed stitches.
To solve this problem, rapid hardening cement is used for the stitching concrete so as to
shorten the time of setting of concrete. Moreover, the stitching work is designed to be carried out at nights of least traffic (Saturday night) and the existing bridge may even be
closed for several hours (e.g. 6 hours) to let the stitching works to left undisturbed.
Sometimes, longitudinal joints are used in connecting new bridge segments to existing
bridges. The main problem associated with this design is the safety concern of vehicles.
The change of frictional coefficients of bridge deck and longitudinal joints when vehicles change traffic lanes is very dangerous to the vehicles. Moreover, maintenance of
longitudinal joints in bridges is quite difficult.


Note: Stitching refers to formation of a segment of bridge deck between an existing bridge and a new bridge.

👇👇👇👇👇👇👇👇👇
@civil_engineers_team

#bridgeworks @civil_engineers_team

Question: What are the advantages of assigning the central pier and the abutment as fixed piers?

(i) For abutment pier to be assigned as fixed pier while the bridge is quite long, the
longitudinal loads due to earthquake are quite large. As the earthquake loads are
resisted by fixed piers, the size of fixed piers will be large and massive. In this connection, for better aesthetic appearance, the selection of abutment as fixed piers could accommodate the large size and massiveness of piers. Normally abutments are
relatively short in height and for the same horizontal force, the bending moment induced is smaller.

(ii) For the central pier to be selected as the fixed pier, the bridge deck is allowed to move
starting from the central pier to the end of the bridge. However, if the fixed pier is located at the abutment, the amount of movement to be incorporated in each bearing due to temperature variation, shrinkage, etc. is more than that when the fixed pier is located at central pier. Therefore, the size of movement joints can be reduced significantly.

👇👇👇👇👇👇👇👇👇
@civil_engineers_team

#bridgeworks @civil_engineers_team

Question: Sometimes the side of concrete bridges is observed to turn black in colour. What is
the reason for this phenomenon?

In some cases, it may be due to the accumulation of dust and dirt. However, for the
majority of such phenomenon, it is due to fungus or algae growth on concrete bridges.
After rainfall, the bridge surface absorbs water and retains it for a certain period of time.
Hence, this provides a good habitat for fungus or algae to grow. Moreover, atmospheric
pollution and proximity of plants provide nutrients for their growth. Improvement in
drainage details and application of painting and coating to bridges help to solve this
problem

👇👇👇👇👇👇👇👇👇
@civil_engineers_team

#bridgeworks @civil_engineers_team

Question: In prestressing work, if more than one wire or strand is included in the same duct, why should all wires/strands be stressed at the same time?

If wires/strands are stressed individually inside the same duct, then those stressed
strand/wires will bear against those unstressed ones and trap them. Therefore, the friction
of the trapped wires is high and is undesirable.

👇👇👇👇👇👇👇👇👇
@civil_engineers_team

These are called as strands
@civil_engineers_team