tornadoes钢筋混凝土结构中英文对照外文翻译文献

中英文对照外文翻译

(

文档含英文原文和中文翻译

)

Reinforced Concrete

Concrete and reinforced concrete are used as building materials in

every

country.

In

many,

including

the

United

States

and

Canada,

reinforced

concrete is a dominant structural material in engineered construction.

The universal nature of reinforced concrete construction stems from the

wide availability of reinforcing bars and the constituents of concrete,

gravel,

sand,

and

cement,

the

relatively

simple

skills

required

in

concrete construction, and the economy of reinforced concrete compared

to

other

forms

of

construction.

Concrete

and

reinforced

concrete

are

used

in bridges, buildings of all sorts underground structures, water tanks,

television towers, offshore oil exploration and production structures,

dams, and even in ships.

Reinforced

concrete

structures

may

be

cast-in-place

concrete,

constructed in their final location, or they may be precast concrete

produced in a factory and erected at the construction site. Concrete

structures

may

be

severe

and

functional

in

design,

or

the

shape

and

layout

and be whimsical and artistic. Few other building materials off the

architect and engineer such versatility and scope.

Concrete is strong in compression but weak in tension. As a result,

cracks develop whenever loads, or restrained shrinkage of temperature

changes, give

rise

to

tensile

stresses in

excess of

the tensile

strength

of the concrete. In a plain concrete beam, the moments about the neutral

axis

due

to

applied

loads

are

resisted

by

an

internal

tension-compression

couple

involving

tension

in

the

concrete.

Such

a

beam

fails

very

suddenly

and

completely

when

the

first

crack

forms.

In

a

reinforced

concrete

beam,

steel bars are embedded in the concrete in such a way that the tension

forces needed for moment equilibrium after the concrete cracks can be

developed in the bars.

The construction of a reinforced concrete member involves building

a from of mold in the shape of the member being built. The form must be

strong

enough

to

support

both

the weight

and hydrostatic pressure of

the

wet concrete,

and

any

forces

applied to

it

by

workers, concrete

buggies,

wind,

and

so

on.

The

reinforcement

is

placed

in

this

form

and

held

in

place

during the concreting operation. After the concrete has hardened, the

forms

are

removed.

As

the

forms

are

removed,

props

of

shores

are

installed

to support the weight of the concrete until it has reached sufficient

strength to support the loads by itself.

The

designer

must

proportion

a

concrete

member

for

adequate

strength

to

resist

the

loads

and

adequate

stiffness

to

prevent

excessive

deflections. In

beam

must

be

proportioned

so

that it can be constructed.

For

example,

the

reinforcement

must

be

detailed

so

that

it

can

be

assembled

in the field, and since the concrete is placed in the form after the

reinforcement is in place, the concrete must be able to flow around,

between,

and

past

the

reinforcement

to

fill

all

parts

of

the

form

completely.

The

choice

of

whether

a

structure

should

be

built

of

concrete,

steel,

masonry,

or

timber

depends

on

the

availability

of

materials

and

on

a

number

of

value

decisions.

The

choice

of

structural

system

is

made

by

the

architect

of

engineer

early

in

the

design,

based

on

the

following

considerations:

1. Economy.

Frequently, the foremost consideration is the overall

const of the structure. This is, of course, a function of the costs of

the

materials

and

the

labor

necessary

to

erect

them.

Frequently,

however,

the overall cost is affected as much or more by the overall construction

time since the contractor and owner must borrow or otherwise allocate

money

to

carry

out

the

construction

and

will

not

receive

a

return

on

this

investment until

the

building

is

ready for

occupancy. In a typical

large

apartment

of

commercial

project,

the

cost

of

construction

financing

will

be

a

significant

fraction

of

the

total

cost.

As

a

result,

financial

savings

due

to

rapid

construction

may

more

than

offset

increased

material

costs.

For this reason, any measures the designer can take to standardize the

design and forming will generally pay off in reduced overall costs.

In many cases the long-term economy of the structure may be more

important than the first cost. As a result, maintenance and durability

are important consideration.

2.

Suitability

of

material

for

architectural

and

structural

function.

A reinforced concrete system frequently allows the designer to combine

the architectural and structural functions. Concrete has the advantage

that it is placed in a plastic condition and is given the desired shape

and

texture

by

means

of

the

forms

and

the

finishing

techniques.

This

allows

such

elements

ad

flat

plates

or

other

types

of

slabs

to

serve

as

load-bearing

elements

while

providing

the

finished

floor

and

/

or

ceiling

surfaces.

Similarly,

reinforced

concrete

walls

can

provide

architecturally

attractive

surfaces

in

addition

to

having

the

ability

to

resist gravity, wind, or seismic loads. Finally, the choice of size of

shape

is

governed

by

the

designer

and

not

by

the

availability

of

standard

manufactured members.

3. Fire resistance. The structure in a building must withstand the

effects

of

a

fire

and

remain

standing

while

the

building

is

evacuated

and

the

fire

is

extinguished.

A

concrete

building

inherently

has

a

1-

to

3-hour

fire rating without special fireproofing or other details. Structural

steel or timber buildings must be fireproofed to attain similar fire

ratings.

4.

Low

maintenance.

Concrete

members

inherently

require

less

maintenance

than

do

structural

steel

or

timber

members.

This

is

particularly true if dense, air- entrained concrete has been used for

surfaces exposed to the atmosphere, and if care has been taken in the

design to provide adequate drainage off and away from the structure.

Special precautions must be taken for concrete exposed to salts such as

deicing chemicals.

5. Availability of materials.

Sand, gravel, cement, and concrete

mixing facilities are very widely available, and reinforcing steel can

be transported to most job sites more easily than can structural steel.

As a result, reinforced concrete is frequently used in remote areas.

On the other hand, there are a number of factors that may cause one

to select a material other than reinforced concrete. These include:

1.

Low

tensile

strength.

The

tensile

strength

concrete

is

much

lower

than

its

compressive

strength

(

about

1/10

),

and

hence

concrete

is

subject

to cracking. In structural uses this is overcome by using reinforcement

to

carry

tensile

forces

and

limit

crack

widths

to

within

acceptable

values.

Unless care is taken in design and construction, however, these cracks

may

be

unsightly

or

may

allow

penetration

of

water.

When

this

occurs,

water

or

chemicals

such

as

road

deicing

salts

may

cause

deterioration

or

staining of the concrete. Special design details are required in such

cases. In the case of water-retaining structures, special details and /

of prestressing are required to prevent leakage.

2. Forms and shoring.

The construction of a cast-in-place structure

involves three steps not encountered in the construction of steel or

timber structures. These are ( a ) the construction of the forms, ( b )

the removal of these

forms, and (c) propping or shoring the new concrete

to

support

its

weight

until

its

strength

is

adequate.

Each

of

these

steps

involves

labor

and

/

or

materials,

which

are

not

necessary

with

other

forms

of construction.

3.

Relatively

low

strength

per

unit

of

weight

for

volume.

The

compressive

strength

of

concrete

is

roughly

5

to

10%

that

of

steel,

while

its unit density is roughly 30% that of steel. As a result, a concrete

structure requires

a

larger

volume

and

a

greater weight

of material

than

does

a

comparable

steel

structure.

As

a

result,

long-span

structures

are

often built from steel.

4.

Time-dependent

volume

changes.

Both

concrete

and

steel

undergo-approximately

the

same

amount

of

thermal

expansion

and

contraction. Because there is less mass of steel to be heated or cooled,

and because steel is a better concrete, a steel structure is generally

affected by temperature changes to a greater extent than is a concrete

structure.

On

the

other

hand,

concrete

undergoes

frying

shrinkage,

which,

if

restrained,

may

cause

deflections

or

cracking.

Furthermore,

deflections will tend to increase with time, possibly doubling, due to

creep of the concrete under sustained loads.

In

almost

every

branch

of

civil

engineering

and

architecture

extensive

use

is

made

of

reinforced

concrete

for

structures

and

foundations.

Engineers

and

architects

requires

basic

knowledge

of

reinforced concrete design throughout their professional careers. Much

of this text is directly concerned with the behavior and proportioning

of

components

that

make

up

typical

reinforced

concrete

structures-beams,

columns, and slabs. Once the behavior of these individual elements is

understood, the designer will have the background to analyze and design

a wide range of complex structures, such as foundations, buildings, and

bridges, composed of these elements.

Since reinforced concrete is a no homogeneous material that creeps,

shrinks, and cracks, its stresses cannot be accurately predicted by the

traditional equations derived in a course in strength of materials for

homogeneous elastic materials. Much of reinforced concrete design in

therefore

empirical,

i.e.,

design

equations

and

design

methods

are

based

on

experimental

and

time-proved

results

instead

of

being

derived

exclusively from theoretical formulations.

A

thorough

understanding

of

the

behavior

of

reinforced

concrete

will

allow the designer to convert an otherwise brittle material into tough

ductile structural elements and thereby take advantage of concrete

’s

desirable

characteristics,

its

high

compressive

strength,

its

fire

resistance, and its durability.

Concrete,

a

stone

like

material,

is

made

by

mixing

cement,

water,

fine

aggregate

(

often

sand

),

coarse

aggregate,

and

frequently

other

additives

( that modify properties ) into a workable mixture. In its unhardened or

plastic

state,

concrete

can

be

placed

in

forms

to

produce

a

large

variety

of structural elements. Although the hardened concrete by itself, i.e.,

without any reinforcement, is strong in compression, it lacks tensile

strength and therefore cracks easily. Because unreinforced concrete is

brittle,

it

cannot

undergo

large

deformations

under

load

and

fails

suddenly-without warning. The addition fo steel reinforcement to the

concrete

reduces

the

negative

effects of

its

two

principal

inherent

weaknesses,

its

susceptibility

to

cracking

and

its

brittleness.

When

the

reinforcement is strongly bonded to the concrete, a strong, stiff, and

ductile

construction

material

is

produced.

This

material,

called

reinforced

concrete,

is

used

extensively

to

construct

foundations,

structural frames, storage takes, shell roofs, highways, walls, dams,

canals,

and

innumerable

other

structures

and

building

products.

Two

other

characteristics

of

concrete

that

are

present

even

when

concrete

is

reinforced are shrinkage and creep, but the negative effects of these

properties can be mitigated by careful design.

A code is a set technical specifications and standards that control

important details of design and construction. The purpose of codes it

produce structures so that the public will be protected from poor of

inadequate and construction.

Two types f coeds exist. One type, called a structural code, is

originated

and

controlled

by

specialists

who

are

concerned

with

the

proper

use of a specific material or who are involved with the safe design of

a particular class of structures.

The second type of code, called a building code, is established to

cover

construction

in

a

given

region,

often

a

city

or

a

state.

The

objective of a building code is also to protect the public by accounting

for

the

influence

of

the

local

environmental

conditions

on

construction.

For

example,

local

authorities

may

specify

additional

provisions

to

account

for

such

regional

conditions

as

earthquake,

heavy

snow,

or

tornados.

National

structural

codes

genrally

are

incorporated

into

local

building codes.

The American Concrete Institute ( ACI ) Building Code covering the

design

of

reinforced

concrete

buildings.

It

contains

provisions

covering

all

aspects

of

reinforced

concrete

manufacture,

design,

and

construction.

It

includes

specifications

on

quality

of

materials,

details

on

mixing

and

placing

concrete,

design

assumptions

for

the

analysis

of

continuous

structures, and equations for proportioning members for design forces.

All structures must be proportioned so they will not fail or deform

excessively under any possible condition of service. Therefore it is

important

that

an

engineer

use

great

care

in

anticipating

all

the

probable