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外文文献原稿及译文

外文文献原稿及译文
外文文献原稿及译文

外文文献原稿和译文

原稿

About Programmable Logiccontrollers(PLCs)

PLCs (programmable controller) is used in a variety of automatic control system and process control hub.They contain multiple input and output, input and output is used to transistors and other circuit, analog switch and relay to control the equipment.PLC software interface, standard calculator interface, specialized language programming and network equipment.

Programmable logic controller I/O channel rules including all input output contact and contact, to expand capacity and the largest number of channels.Contact number is the sum of input and output points.PLC can specify any combination of these values.Extension units can be stack or connected to each other to increase the total control.The largest number of channels are in an extension system, the total number of maximum input and output channels.PLC system rules include scanning time, number of instructions, data storage and storage program.Scan time is used to monitor input and output module of PLC need time.Standard operation instruction is used in PLC software.Data storage is the ability to store data.Program memory is the ability to control software.

Used for programmable controller input devices including DC, AC, intermediate relay, thermocouple, RTD, frequency or pulse, transistors and interrupt signal input;Output devices include DC, AC, intermediate relay, frequency or pulse, transistor, three-terminal two-way thyristor switch components;PLC programming equipment including control panel, handle and computer.

Programmable control is used to control a variety of software programming language.These languages including iec61131-3, sequential table (SFC), action block diagram (FBD), ladder diagram (LD), and the structure of the text (ST), instruction sequences (IL), relay ladder diagram (RIL), flow charts, C language and Basic language.Iec61131-3 programming environment can support five languages, with international standards to regulate, SFC, respectively, FBD, LD, ST and IL.This allows more vendor compatibility and a variety of languages.SFC is a kind of graph

language, it provides the programming in order to cooperate, can support the order selection and tied for choice, to choose between them.Runtime FBD with a big, established the complicated process, in the form of graphs.Standard mathematical and logical operation can be combined with user interaction and interface operation.LD is suitable for discrete control and interlock logic diagram language.It is fully compatible with FBD on discrete control.ST is a kind of text language, used for complex mathematical and computational process, language is not applicable to chart.IL is similar to the combination of coding low-level languages.It is used in relatively simple logical instructions.Relay ladder diagram and ladder diagram is used for programmable controller is an important programming https://www.wendangku.net/doc/7f19048548.html,dder diagram programming is designed to relay logic diagram representation of the program.Flow chart is a graphic language, for use in a controller or operations described in the order of application software, it is used to establish a standard component of recycled runtime.C language is a high-level programming language, suitable for processing the most complicated calculation, a continuous data acquisition task.It typically run in PC debugging.BASIC language is used to handle the number of consecutive data acquisition and interface operation of high-level language.

Programmable controller also specification of many computer interface equipment, network rules and characteristics.PLC energy equipment and running environment is also very important.

The development history of programmable controller

In 1968, general motors (GM), according to the needs of the development of the market situation and put forward the "many varieties, small batch, new car brand model" strategy.To implement this strategy, relying on the original industrial control device obviously not, and there must be a kind of new industrial control device, it can be with the change of the products, flexible and easily change control scheme to difficult to meet the different requirements of control.

In 1969, the famous American digital equipment corporation (DEC) according to the function requirements of GM, developed the new industrial control device, and the GM of a vehicle to run automated production line for the first time to succeed.According to this new type of industrial control devices can be programmed

to change control scheme this characteristic, and the situation of the specialized for Logic control, says the new industrial control device for the Programmable control (Programmable Logic Controller), hereinafter referred to as PLC.

From 1968 to now, the PLC has experienced four generation: most of the first generation of PLC with a machine development, with the core memory storage, only the logic control function.In the second generation of PLC products for 8-bit microprocessor and semiconductor memory, PLC product seriation.The third generation of PLC product with high performance microprocessor and chip is used in great quantities in the PLC CPU, PLC speed greatly improved, thus enabling it to develop in the direction of multi-function communications and networking.The fourth generation of PLC products not only comprehensive use 16-bit and 32-bit

high-performance microprocessors, high-performance slice microcontroller processor, RISC (Reduced instruction set computer) Reduced instruction system CPU and other advanced CPU, and more than one processor in a PLC configuration, multi-channel processing.Also produced a large number of embedded microprocessor module, only makes the fourth generation of PLC product has the function of logical control, process control, motion control, data control, networked control functions really worthy of the name of multi-functional controller.At the same time, the PLC network composed of PLC has also been rapid development.PLC and industrial control of PLC network in factory enterprises become the preferred device, composed of PLC

multi-stage distributed PLC network become indispensable fundamental part of CIMS system.People spoke highly of the importance of PLC and its network, it is one of the three pillars of modern.

Selecting machine model

Market popular PLC products manufacturer in China with the following companies:

(1) schneider company, including the introduction of early from Modicon company by the tianjin instrument instrument and meter plant products, products are now Quantum, Premium and Momentum;

(2) rockwell company (including AB company) PLC products, products are now SLC and Micro Logix Control Logix etc.

(3) of Siemens PLC products, products are now 400/300 / S7-200 series;

(4) ge PLC products;

(5) the company's products such as omron, mitsubishi, Fuji, panasonic, one of the most popular is the mitsubishi FX series.

The basic principle of PLC selection is: in the input/output quantity meet the requirements under the premise of should choose the most reliable, maintenance, and use the most convenient and cost-effective optimal products.

Selecting I/O

PLC is an industrial control system, the control object is industrial production equipment or the production process of industrial products, working environment is the industrial production field.It connects the industrial production process is achieved by I/O interface module.PLC has a lot of I/O interface module including switch input module, the switch output module, analog input module and analog output module and special module, we should use according to the characteristics of their implementation options.

(1) determine the number of input/output

According to the requirements of the control system, determine the number of input/output required, should increase the spare quantity of 10% 20%, in order to increase control function in any time.

(2) the switch quantity input/output

Switch input/output interface and can take the signals from the sensors and switches and control equipment.A typical 24-240 - v ac input/output signals, 5-240 - v dc input/output signals.

(3) the analog input/output

Analog input/output inte rface can accept the signal generated by the

sensor.These interfaces can be used to measure turnover rate, temperature and pressure, and thus to control the voltage or current output device.Range for these interfaces - 10-10 v, + 0 to 10 v, 4-20 ma, or 10 to 50 ma.

Some manufacturers on the PLC design special dedicated analog interface, so it can receive low level signal.In general, this interface module can be used to receive different types of thermocouple and RTD mixed signal.

(4) special function input/output

When selecting a PLC, user may faced some special types of input/output and some because of the location of the limited input/output and fast response and frequency problem caused by the non standard input/output.Now, the user should consider whether to accept by the market or manufacturers to provide a special module, through a dedicated part of the module and dispose data, so as to reduce the use of the CPU, improve the efficiency of the task processing, to minimize failure caused by high limit control.

PLC status

In a PLC, the lack of keyboard and other input and output devices is a very worthy of attention.In PLC front usually have a certain amount of status https://www.wendangku.net/doc/7f19048548.html,ually indicates that:

The start-up - as long as the PLC charged, it will be started.

Program is running - this will indicate whether running or if no program is running. Error display - when PLC has a large hardware or software errors, it will be displayed. These lights are usually used for debugging.A certain number of button will also be provided to the PLC hardware.The most common button is a run/programming selection switch, when in keeping the state, it will be transferred to the programming;When the production status, it will be transferred to the operation.A PLC system almost no start closing switch or reset switch at the front.It needs to be designed into the system the rest.

The state of the PLC can also be ladder logic diagram.Test whether the program implemented is very common for the first time.'first scan input in ladder diagram by scanning for the first time, will is right, and in the rest of the time when the scanning is wrong.In this case, the PLC - 5 'first scan' address is' S2:1/14 '.According to the example of the logical relationship, the first scan will seal the 'light' until the 'clear' is started.So the light will be start brighter in the PLC, but after the "clear" is launched, it will shut down and remain in the closed position.'first scan module is mentioned in the "first pass" module.

PLC application domain

At home and abroad at present, the PLC has been widely used in steel, petroleum, chemical, electric power, building materials, machinery manufacturing, automobile, textile, transportation, environmental protection and cultural industries with happiness and usage can be roughly divided into the following categories:

(1) the switch quantity logic control

This is the most basic, the most widely PLC applications, it replaces the traditional relay circuit, realize logic control, sequence control, can be used for control of single equipment, also can be used in many machines and automatic assembly line.Such as injection molding machine, printing machine, stapler machinery, combined machine tool, grinding machine, packaging production line, plating production line, etc.

(2) analog control

In the process of industrial production, there are a lot of continuous change, such as temperature, pressure, flow, liquid level and speed and so on are all analog.In order to make the programmable controller to deal with analog, must implement the analog quantity and digital quantity between A/D and D/A conversion module, the programmable controller for analog control.

(3) motion control

PLC can be used in circular motion and linear motion control.From control mechanism configuration, early applied directly to switch the I/O module connection position sensors and actuators, now in general use special motion control

module.Such as driving a stepper motor or servo motor of uniaxial or multi-axis position control module.The world's major products almost all have motion control function of PLC manufacturers, widely used in all kinds of machinery, machine tools, robots, elevators, etc.

(4) process control

Process control is to point to the analog quantities such as temperature, pressure, flow rate of the closed loop control.As industrial control computer, PLC can prepare the all kinds of control algorithm procedures, complete the closed-loop control.PID control is generally be applied closed loop control system of the control https://www.wendangku.net/doc/7f19048548.html,rge and medium-sized PLC has PID module, at present many small PLC also has the

function module.PID processing is generally run special PID subroutine.The process control in metallurgy, chemical industry, heat treatment, boiler control occasions has wide application, etc.

(5) the data processing

Modern PLC with mathematical operation, data transmission, data conversion, sorting, look-up table, a function, such as the operation can complete data collection, analysis, and processing.These data can be compared with the reference value of memory, accomplish a certain number of control operation, also can send to other intelligent device, the use of communication function or printing them tabulation.Data processing is generally used in a large control system, such as unmanned control of flexible manufacturing systems;Can also be used to process control system, such as paper making, metallurgy, food industry, some of the large control system.

(6) communications and networking

PLC communication with the communication between PLC and the communication between PLC and other smart devices.With the development of computer control, factory automation network is growing fast, the PLC manufacturers have attached great importance to PLC communications functions, have launched their own network systems.The newly production PLC has a communication interface, communication is very convenient.

PLC application field is still in the extension, in Japan, the application of PLC has been from the traditional industrial automatic control equipment and machinery, extended to the following areas of application: small and medium-sized process control system, remote maintenance service system, the energy conservation monitoring control system, and of the relation of living machines, relationship with the environment, and all have rapidly rising trend.It is important to note that with PLC, DSC mutual penetration, both the boundaries of an increasingly fuzzy, PLC applied to discrete manufacturing industry from the traditional to the applied to the continuous process industries to expand.

译文

PLC介绍

PLC(可编程控制器)是用于各种自动控制系统和过程的可控网络集线器。他们包含多个输入输出,输入输出是用于晶体管和其它电路,模拟开关和继电器来控制设备的。PLC用软件接口,标准计算器接口,专门的语言和网络设备编程。

可编程逻辑控制器I/O通道规则包括所有的输入触点和输出触点,拓展能力和最大数量的通道。触点数量是输入点和输出点的总和。PLC可以指定这些值的任何可能的组合。扩展单元可以被堆栈或互相连接来增加总的控制能力。最大的数量的通道是在一个扩展系统中输入和输出通道的最大总数量。PLC系统规则包括扫描时间,指令数量,数据存储和程序存储。扫描时间是PLC需要的用来监测输入输出模块的时间。指令是用于PLC软件的标准操作。数据存储是存储数据的能力。程序存储是控制软件的能力。

用于可编程控制器的输入设备包括DC,AC,中间继电器,热电偶,RTD,频率或脉冲,晶体管和中断信号输入;输出设备包括DC,AC,中间继电器,频率或脉冲,晶体管,三端双向可控硅开关元件;PLC的编程设备包括控制面板,手柄和计算机。

可编程控制器用各种软件编程语言来控制。这些语言包括IEC61131-3,顺序执行表(SFC),动作方块图(FBD),梯形图(LD),结构文本(ST),指令序列(IL),继电器梯形图(RIL),流程图,C语言和Basic语言。IEC61131-3编程环境能支持五种语言,用国际标准加以规范,分别为SFC,FBD,LD,ST和IL。这便允许了多卖主兼容性和多种语言编程。SFC是一种图表语言,它提供了编程顺序的配合,能支持顺序选择和并列选择,二者择其一即可。FBD用一种大的运行库,以图表形式建立了一些复杂的过程。标准数学和逻辑运行可以与用户交流和接口运行相结合。LD是适合于离散控制和互锁逻辑的图表语言。它在离散控制上与FBD是完全兼容的。ST是一种文本语言,用于复杂的数学过程和计算,不太适用于图表语言。IL是与组合编码相似的低级语言。它用在相对比较简单的逻辑指令。继电器梯形图或梯形图是是用于可编程控制器的重要的编程语言。梯形图编程是设计成继电器逻辑程序的图表表示法。流程图是一种图表语言,用于在一个控制器或应用软件中描述顺序操作,它用于建立有标准组件的可循环使用的运行库。C语言是一种高级编程语言,适用于处理最复杂的计算,连续的数据采集任务。它典型地在PC机上运行调试。BASIC语言是用于处理数据的连续的数字采集和接口运行的高级语言。

可编程控制器也规范了许多计算机接口设备,网络规则和特色。PLC能源设备和运行环境也是非常重要的。

可编程控制器及其网络的发展历史

1968年,美国通用汽车公司(GM)根据市场形势与发展的需要,提出了“多品种、小批量、不断翻新汽车品牌型号”的战略。要实现这个战略决策,依靠原有的工业控制装置显然不行,而必须有一种新的工业控制装置,它可以随着生产品种的改变,灵活方便地改变控制方案以难以满足对控制的不同要求。

1969年,着名的美国数字设备公司(DEC)根据GM的功能要求,研制出了这种新的工业控制装置,并在GM公司的一条汽车自动化生产线上首次运行取得成功。根据这种新型工业控制装置可以通过编程改变控制方案这一特点,以及专门用于逻辑控制的情况,称这种新的工业控制装置为可编程序控制(Programmable Logic Controller),简称PLC。

从1968年到现在,PLC经历了四次换代:第一代PLC大多用一位机开发,用磁芯存储器存储,只有逻辑控制功能。在第二代PLC产品中换成了8位微处理器及半导体储存器,PLC产品开始系列化。第三代PLC产品随着高性能微处理器及位片式CPU在PLC中大量使用,PLC的速度大大提高,从而促使它向多功能及联网通信方向发展。第四代PLC产品不仅全面使用16位、32位高性能微处理器,高性能位片式微处理器,RISC(Reduced instruction set computer)精简指令系统CPU等高级CPU,而且在一台PLC中配置多个处理器,进行多通道处理。同时产生了大量内含微处理器的只能模块,使得第四代PLC产品成为具有逻辑控制功能、过程控制功能、运动控制功能、数据控制功能、联网控制功能的真正名副其实的多功能控制器。同一时期,由PLC组成的PLC网络也得到飞速发展。PLC与PLC网络成为工厂企业中首选的工业控制装置,由PLC组成的多级分布式PLC网络成为CIMS系统不可或缺的基本组成部分。人们高度评价PLC及其网络的重要性,认为它是现代化的三大支柱之一。

选择模型

我国的市场流行的PLC产品的生产厂家有以下几个公司:

(1)施耐德公司,包括引进自Modicon公司由早期天津仪器仪表厂的产品,现在的产品有Quantum,Premium和Momentum;

(2)罗克韦尔公司(包括AB公司)PLC产品,现在的产品有SLC、Micro Logix 和Control Logix等;

(3)西门子公司的PLC产品,现在的产品有S7-400/300/200等系列;

(4)通用电气公司PLC产品;

(5)日本公司的产品如欧姆龙,三菱,富士,松下,其中最受欢迎的是三菱公司的FX系列。

PLC选型的基本原理是:在输入/输出数量满足要求的前提下应选择最可靠、维护和使用最方便以及性价比最优的产品。

输入/输出选择

PLC是一种工业控制系统,其控制对象是工业生产设备或工业产品生产过程、工作环境是工业生产现场。它连接的工业生产过程是通过I/O接口模块实现。PLC有很多I/O接口模块包括开关量输入模块、开关量输出模块、模拟量输入模块和模拟量输出模块以及一些特殊的模块,使用时我们应该根据他们的特点执行选项。

(1)确定输入/输出数量

根据控制系统的需求,确定所需输入/输出的数量,应增加备用量的

10%-20%,为了能在任何时间增加控制功能。

(2)开关量输入/输出

开关量输入/输出接口可以从传感器和开关和控制设备接受信号。典型的交流输入/输出信号24-240V,直流输入/输出信号5-240V。

(3)模拟量输入/输出

模拟量输入/输出接口可以接受由传感器产生的信号。这些接口可以用于测量流动率、温度和压力,并以此来控制由电压或电流的输出设备。这些接口的量程为-10- +10V、0-10V、4-20mA或10-50mA。

有些厂家在PLC上设计了特殊的专用模拟接口,因此它可以接收低电平信号。一般来说,这种接口模块可以用于接收不同类型的热电偶或RTD混合信号。

(4)特殊功能输入/输出

当选择一个PLC,用户可能面临一些特殊类型的输入/输出还有一些因为有限的输入/输出的位置和快速响应以及频率问题造成的非标准的输入/输出。现在,用户应该考虑是否接受由市场或制造商提供的专用模块,通过专用模块自行处理一部分的数据,从而减少CPU的使用,提高任务处理的效率,以最大限度降低因高温限制造成的控制失灵。

PLC状态显示

在一个PLC中,缺少键盘和其他的输入输出设备是非常值得注意的。在PLC 前端通常有一定数量的状态指示灯。通常指示灯表明:

电源启动—只要PLC带电,它将被启动。

程序运行—这将指示是否正在运行或是否没有程序正在运行。

错误显示—当PLC有大的硬件或软件错误时,这将有显示。

这些灯通常用于调试。一定数量的按钮也将提供给PLC的硬件。最普通的按钮是一个运行/编程选择开关,当在保持状态时,它将被调到编程;当在生产状态时,它将被调到运行。一个PLC系统几乎没有一个启动关闭开关或复位开关在前面。这需要被设计到系统剩余部分。

PLC的状态也能被梯形逻辑图检测。检测程序是否第一次被执行是非常普遍的。‘first scan’输入在梯形图被第一次扫描时,将是对的,而在其余的每次扫描时是错误的。这种情况下,PLC—5的‘first scan’的地址是

‘S2:1/14’。根据例子中的逻辑关系,第一次扫描将封上‘light’直到

‘clear’被启动。因此灯将在PLC被启动之后变亮,但在‘clear’被启动之后,它将关闭并且保持在关闭状态。‘first scan’模块在‘first pass’模块中被提到。

PLC应用领域

目前,PLC在国内外已广泛应用于钢铁、石油、化工、电力、建材、机械制造、汽车、轻纺、交通运输、环保及文化与快乐等行业,使用情况大致可归纳为如下几类:

(1)开关量的逻辑控制

这是PLC最基本、最广泛的应用领域,它取代了传统的继电器电路,实现逻辑控制、顺序控制,既可用于单台设备的控制,也可用于多机群及自动化流水线。如注塑机、印刷机、订书机械、组合机床、磨床、包装生产线、电镀流水线等。

(2)模拟量控制

在工业生产过程中,有许多连续变化的量,如温度、压力、流量、液位和速度等都是模拟量。为了使可编程控制器处理模拟量,必须实现模拟量和数字量之间A/D和D/A转换模块,使可编程控制器用于模拟量控制。

(3)运动控制

PLC可用于圆周运动或直线运动的控制。从控制机构配置来说,早期直接用于开关量I/O模块连接位置传感器和执行机构,现在一般使用专用的运动控制模块。如可驱动步进电机或伺服电机的单轴或多轴位置控制模块。世界上各主要PLC厂家的产品几乎都有运动控制功能,广泛用于各种机械、机床、机器人、电梯等场合。

(4)过程控制

过程控制是指对温度、压力、流量等模拟量的闭环控制。作为工业控制计算机,PLC能编制各种各样的控制算法程序,完成闭环控制。PID调节是一般闭环控制系统中用得较多的控制方法。大中型PLC都有PID模块,目前许多小型PLC也具有此功能模块。PID处理一般是运行专门的PID子程序。过程控制在冶金、化工、热处理、锅炉控制等场合有广泛的应用。

(5)数据处理

现代PLC具有数学运算、数据传送、数据转换、排序、查表、位操作等功能,可以完成数据的采集、分析、及处理。这些数据可以与存储器中的参考值比较,完成一定的控制操作,也可以利用通信功能传送到别的智能装置,或将它们打印制表。数据处理一般用于大型控制系统,如无人控制的柔性制造系统;也可用于过程控制系统,如造纸、冶金、食品工业中的一些大型控制系统。

(6)通信及联网

PLC通信含PLC间的通信及PLC与其它智能设备间的通信。随着计算机控制的发展,工厂自动化网络发展得很快,各PLC厂商都十分重视PLC的通信功能,纷纷推出各自的网络系统。新近生产的PLC都具有通信接口,通信非常方便。

PLC的应用领域仍在扩展,在日本,PLC的应用范围已从传统的产业设备和机械的自动控制,扩展到以下应用领域:中小型过程控制系统、远程维护服务系统、节能监视控制系统,以及与生活关连的机器、与环境关连的机器,而且均有急速上升趋势。值得注意的是,随着PLC、DSC互相渗透,二者的界线日趋模糊的时候,PLC从传统的应用于离散的制造业向应用到连续的流程工业扩展。

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华北电力大学科技学院 毕业设计(论文)附件 外文文献翻译 学号:121912020115姓名:彭钰钊 所在系别:动力工程系专业班级:测控技术与仪器12K1指导教师:李冰 原文标题:Infrared Remote Control System Abstract 2016 年 4 月 19 日

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文献翻译 原文 Combining JSP and Servlets The technology of JSP and Servlet is the most important technology which use Java technology to exploit request of server, and it is also the standard which exploit business application .Java developers prefer to use it for a variety of reasons, one of which is already familiar with the Java language for the development of this technology are easy to learn Java to the other is "a preparation, run everywhere" to bring the concept of Web applications, To achieve a "one-prepared everywhere realized." And more importantly, if followed some of the principles of good design, it can be said of separating and content to create high-quality, reusable, easy to maintain and modify the application. For example, if the document in HTML embedded Java code too much (script), will lead the developed application is extremely complex, difficult to read, it is not easy reuse, but also for future maintenance and modification will also cause difficulties. In fact, CSDN the JSP / Servlet forum, can often see some questions, the code is very long, can logic is not very clear, a large number of HTML and Java code mixed together. This is the random development of the defects. Early dynamic pages mainly CGI (Common Gateway Interface, public Gateway Interface) technology, you can use different languages of the CGI programs, such as VB, C / C + + or Delphi, and so on. Though the technology of CGI is developed and powerful, because of difficulties in programming, and low efficiency, modify complex shortcomings, it is gradually being replaced by the trend. Of all the new technology, JSP / Servlet with more efficient and easy to program, more powerful, more secure and has a good portability, they have been many people believe that the future is the most dynamic site of the future development of technology. Similar to CGI, Servlet support request / response model. When a customer submit a request to the server, the server presented the request Servlet, Servlet responsible for handling requests and generate a response, and then gave the server, and then from the server sent to

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外文文献: Designing Against Fire Of Buliding John Lynch ABSTRACT: This paper considers the design of buildings for fire safety. It is found that fire and the associ- ated effects on buildings is significantly different to other forms of loading such as gravity live loads, wind and earthquakes and their respective effects on the building structure. Fire events are derived from the human activities within buildings or from the malfunction of mechanical and electrical equipment provided within buildings to achieve a serviceable environment. It is therefore possible to directly influence the rate of fire starts within buildings by changing human behaviour, improved maintenance and improved design of mechanical and electrical systems. Furthermore, should a fire develops, it is possible to directly influence the resulting fire severity by the incorporation of fire safety systems such as sprinklers and to provide measures within the building to enable safer egress from the building. The ability to influence the rate of fire starts and the resulting fire severity is unique to the consideration of fire within buildings since other loads such as wind and earthquakes are directly a function of nature. The possible approaches for designing a building for fire safety are presented using an example of a multi-storey building constructed over a railway line. The design of both the transfer structure supporting the building over the railway and the levels above the transfer structure are considered in the context of current regulatory requirements. The principles and assumptions associ- ated with various approaches are discussed. 1 INTRODUCTION Other papers presented in this series consider the design of buildings for gravity loads, wind and earthquakes.The design of buildings against such load effects is to a large extent covered by engineering based standards referenced by the building regulations. This is not the case, to nearly the same extent, in the

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PA VEMENT PROBLEMS CAUSED BY COLLAPSIBLE SUBGRADES By Sandra L. Houston,1 Associate Member, ASCE (Reviewed by the Highway Division) ABSTRACT: Problem subgrade materials consisting of collapsible soils are com- mon in arid environments, which have climatic conditions and depositional and weathering processes favorable to their formation. Included herein is a discussion of predictive techniques that use commonly available laboratory equipment and testing methods for obtaining reliable estimates of the volume change for these problem soils. A method for predicting relevant stresses and corresponding collapse strains for typical pavement subgrades is presented. Relatively simple methods of evaluating potential volume change, based on results of familiar laboratory tests, are used. INTRODUCTION When a soil is given free access to water, it may decrease in volume, increase in volume, or do nothing. A soil that increases in volume is called a swelling or expansive soil, and a soil that decreases in volume is called a collapsible soil. The amount of volume change that occurs depends on the soil type and structure, the initial soil density, the imposed stress state, and the degree and extent of wetting. Subgrade materials comprised of soils that change volume upon wetting have caused distress to highways since the be- ginning of the professional practice and have cost many millions of dollars in roadway repairs. The prediction of the volume changes that may occur in the field is the first step in making an economic decision for dealing with these problem subgrade materials. Each project will have different design considerations, economic con- straints, and risk factors that will have to be taken into account. However, with a reliable method for making volume change predictions, the best design relative to the subgrade soils becomes a matter of economic comparison, and a much more rational design approach may be made. For example, typical techniques for dealing with expansive clays include: (1) In situ treatments with substances such as lime, cement, or fly-ash; (2) seepage barriers and/ or drainage systems; or (3) a computing of the serviceability loss and a mod- ification of the design to "accept" the anticipated expansion. In order to make the most economical decision, the amount of volume change (especially non- uniform volume change) must be accurately estimated, and the degree of road roughness evaluated from these data. Similarly, alternative design techniques are available for any roadway problem. The emphasis here will be placed on presenting economical and simple methods for: (1) Determining whether the subgrade materials are collapsible; and (2) estimating the amount of volume change that is likely to occur in the 'Asst. Prof., Ctr. for Advanced Res. in Transp., Arizona State Univ., Tempe, AZ 85287. Note. Discussion open until April 1, 1989. To extend the closing date one month,

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