新鲜事物钢筋混凝土中英文资料外文翻译文献

钢筋混凝土

中英文资料翻译

1

外文翻译

1.1 Reinforced Concrete

Plain concrete is formed from a hardened mixture of cement ,water ,fine aggregate,

coarse

aggregate

(crushed

stone

or

gravel),air,

and

often

other

admixtures.

The

plastic

mix is placed and consolidated in the formwork, then cured to facilitate the acceleration

of

the

chemical

hydration

reaction

lf

the

cement/water

mix,

resulting

in

hardened

concrete.

The

finished

product

has

high

compressive

strength,

and

low

resistance

to

tension,

such

that

its

tensile

strength

is

approximately

one

tenth

lf

its

compressive

strength. Consequently, tensile and shear reinforcement in the tensile regions of sections

has to be provided to compensate for the weak tension regions in the reinforced concrete

element.

It

is

this

deviation

in

the

composition

of

a

reinforces

concrete

section

from

the

homogeneity of standard wood or steel sections that requires a modified approach to the

basic

principles

of

structural

design.

The

two

components

of

the

heterogeneous

reinforced

concrete

section

are

to

be

so

arranged

and

proportioned

that

optimal

use

is

made of the materials involved. This is possible because concrete can easily be given any

desired shape by placing and compacting the wet mixture of the constituent ingredients

are

properly

proportioned,

the

finished

product

becomes

strong,

durable,

and,

in

combination

with

the

reinforcing

bars,

adaptable

for

use

as

main

members

of

any

structural system.

The techniques necessary for placing concrete depend on the type of member to be

cast: that is, whether it is a column, a bean, a wall, a slab, a foundation. a mass columns,

or

an

extension

of

previously

placed

and

hardened

concrete.

For

beams,

columns,

and

walls, the forms should be well oiled after cleaning them, and the reinforcement should

be

cleared

of

rust

and

other

harmful

materials.

In

foundations,

the

earth

should

be

compacted and thoroughly moistened to about 6 in. in depth to avoid absorption of the

moisture

present

in

the

wet

concrete.

Concrete

should

always

be

placed

in

horizontal

layers which are compacted by means of high frequency power-driven vibrators of either

the immersion or external type, as the case requires, unless it is placed by pumping. It

must be kept in mind, however, that over vibration can be harmful since it could cause

segregation of the aggregate and bleeding of the concrete.

Hydration

of

the

cement

takes

place

in

the

presence

of

moisture

at

temperatures

above 50

°F. It is necessary to maintain such a condition in order that the

chemical

hydration

reaction

can

take

place.

If

drying

is

too

rapid,

surface

cracking takes place. This would result in reduction of concrete strength

due to cracking as well as the failure to attain full chemical hydration.

It is clear that a large number of parameters have to be dealt with in proportioning a

reinforced

concrete

element,

such

as

geometrical

width,

depth,

area

of

reinforcement,

steel strain, concrete strain, steel stress, and so on. Consequently, trial and adjustment is

necessary in the choice of concrete sections, with assumptions based on conditions at site,

availability of the constituent materials, particular demands of the owners, architectural

and headroom requirements, the applicable codes, and environmental reinforced concrete

is often a site-constructed composite, in contrast to the standard mill-fabricated beam and

column sections in steel structures.

A trial section has to be chosen for each critical location in a structural system. The

trial section has to be analyzed to determine if its nominal resisting strength is adequate

to carry the applied factored load. Since more than one trial is often necessary to arrive at

the

required

section,

the

first

design

input

step

generates

into

a

series

of

trial- and-adjustment analyses.

The trial-and

–

adjustment procedures for the choice of a concrete section lead to the

convergence

of

analysis

and

design.

Hence

every

design

is

an

analysis

once

a

trial

section

is

chosen.

The

availability

of

handbooks,

charts,

and

personal

computers

and

programs supports this approach as a more efficient, compact, and speedy instructional

method

compared

with

the

traditional

approach

of

treating

the

analysis

of

reinforced

concrete separately from pure design.

1.2 Earthwork

Because

earthmoving

methods

and

costs

change

more

quickly

than

those

in

any

other branch of civil engineering, this is a field where there are real opportunities for the

enthusiast.

In

1935

most

of

the

methods

now

in

use

for

carrying

and

excavating

earth

with rubber-tyred equipment did not exist. Most earth was moved by narrow rail track,

now relatively rare, and the main methods of excavation, with face shovel, backacter, or

dragline or

grab, though they

are still widely used are only

a few of the many

current

methods. To keep his knowledge of earthmoving equipment up to date an engineer must

therefore

spend

tine

studying

modern

machines.

Generally

the

only

reliable

up-to-date

information on excavators, loaders and transport is obtainable from the makers.

Earthworks or earthmoving means cutting into ground where its surface is too high

(

cuts

),

and

dumping

the

earth

in

other

places

where

the

surface

is

too

low

(

fills).

Toreduce earthwork costs, the volume of the fills should be equal to the volume of the

cuts and wherever possible the cuts should be placednear to fills of equal volume so as to

reduce transport and double handlingof the fill. This work of earthwork design falls on

the

engineer

who

lays

out

the

road

since

it

is

the

layout

of

the

earthwork

more

than

anything

else

which

decides

its

cheapness.

From

the

available

maps

ahd

levels,

the

engineering

must

try

to

reach

as

many

decisions

as

possible

in

the

drawing

office

by

drawing cross sections of the earthwork. On the site when further information becomes

available he can make changes in jis sections and layout,but the drawing lffice work will

not have been lost. It will have helped him to reach the best solution in the shortest time.

The cheapest way of moving earth is to take it directly out of the cut and drop it as

fill with the same machine. This is not always possible, but when it canbe done it is ideal,

being

both

quick

and

cheap.

Draglines,

bulldozers

and

face

shovels

an

do

this.

The

largest radius is obtained with the dragline,and the largest tonnage of earth is moved by

the bulldozer, though only over short disadvantages of the dragline are that

it must dig below itself, it cannot dig with force into compacted material, it cannot dig on

steep slopws, and its dumping and digging are not accurate.

Face shovels are between bulldozers and draglines, having a larger radius of action

than bulldozers but less than draglines. They are anle to dig into a vertical cliff face in a

way which would be dangerous tor a bulldozer operator and impossible for a dragline.

Each

piece

of

equipment

should

be

level

of

their

tracks

and

for

deep

digs

in

compact

material a backacter is most useful, but its dumping radius is considerably less than that

of the same escavator fitted with a face shovel.

Rubber-tyred

bowl

scrapers

are

indispensable

for

fairly

level

digging

where

the

distance of transport is too much tor a dragline or face shovel. They can dig the material

deeply ( but only below themselves ) to a fairly flat surface, carry it hundreds of meters if

need be, then drop it and level it roughly during the dumping. For hard digging it is often

found economical to keep a pusher tractor ( wheeled or tracked ) on the digging site, to

push

each

scraper

as

it

returns

to

dig.

As

soon

as

the

scraper

is

full,the

pusher

tractor

returns to the beginning of the dig to heop to help the nest scraper.

Bowl scrapers are often extremely powerful machines;many makers build scrapers

of 8 cubic meters struck capacity, which carry 10 m ?

heaped. The largest self-propelled

scrapers are of 19 m ?

struck capacity ( 25 m ?

heaped )and they are driven by a tractor

engine of 430 horse-powers.

Dumpers

are

probably

the

commonest

rubber-tyred

transport

since

they

can

also

conveniently be used for carrying concrete or other building materials. Dumpers have the

earth container over the front axle on large rubber-tyred wheels, and the container tips

forwards on most types, though in articulated dumpers the direction of tip can be widely

varied. The smallest dumpers have a capacity of about 0.5 m ?

, and the largest standard

types are of about 4.5 m ?

. Special types include the self-loading dumper of up to 4 m ?

and

the

articulated

type

of

about

0.5

m

?

.

The

distinction

between

dumpers

and

dump

trucks

must

be

remembered .dumpers

tip

forwards

and

the

driver

sits

behind

the

load.

Dump trucks are heavy, strengthened tipping lorries, the driver travels in front lf the load

and the load is dumped behind him, so they are sometimes called rear-dump trucks.

1.3 Safety of Structures

The

principal

scope

of

specifications

is

to

provide

general

principles

and

computational methods in order to verify safety of structures.

The “ safety factor ”, which

according to modern trends is independent of the nature and combination of the materials

used,

can

usually

be

defined

as

the

ratio

between

the

conditions.

This

ratio

is

also

proportional to the inverse of the probability ( risk ) of failure of the structure.

Failure has to be considered not only as overall collapse of the structure but also as

unserviceability or, according to a more precise. Common definition. As the reaching of a

“

limit state ” which causes the construction not to accomplish the task it was designed

for. There are two categories of limit state :

(1)Ultimate limit

sate, which corresponds

to

the

highest

value of the load-bearing

capacity. Examples include local buckling or global instability of the structure; failure of

some sections and subsequent transformation of the structure into a mechanism; failure

by fatigue; elastic or plastic deformation or creep that cause a substantial change of the

geometry of the structure; and sensitivity of the structure to alternating loads, to fire and

to explosions.

(2)Service limit states, which are functions of the use and durability of the structure.

Examples include excessive deformations and displacements without instability; early or

excessive cracks; large vibrations; and corrosion.

Computational methods used to verify structures with respect to the different safety

conditions can be separated into:

(1)Deterministic

methods,

in

which

the

main

parameters

are

considered

as

nonrandom parameters.

(2)Probabilistic

methods,

in

which the

main

parameters

are

considered

as

random

parameters.

Alternatively,

with

respect

to

the

different

use

of

factors

of

safety,

computational

methods can be separated into:

(1)Allowable stress method, in which the stresses computed under maximum loads

are compared with the strength of the material reduced by given safety factors.

(2)Limit states method, in which the structure may be proportioned on the basis of

its maximum strength. This strength, as determined by rational analysis, shall not be less

than that required to support a factored load equal to the sum of the factored live load and

dead load ( ultimate state ).

The

stresses

corresponding

to

working

(

service

)

conditions

with

unfactored

live

and dead loads are compared with prescribed values ( service limit state ) . From the four

possible

combinations

of

the

first

two

and

second

two

methods,

we

can

obtain

some

useful computational methods. Generally, two combinations prevail:

(1)deterministic methods, which make use of allowable stresses.

(2)Probabilistic methods, which make use of limit states.

The

main

advantage

of

probabilistic

approaches

is

that,

at

least

in

theory,

it

is

possible to

scientifically take into account

all random

factors of safety,

which are then

combined to define the safety factor. probabilistic approaches depend upon :

(1) Random

distribution

of

strength

of

materials

with

respect

to

the

conditions

of