《第四節(jié)：壓桿的穩(wěn)定計(jì)算（一）》單元教學(xué)設(shè)計(jì)

1、工程力學(xué)單元教學(xué)設(shè)計(jì)水工建筑物教學(xué)文本壓桿的穩(wěn)定計(jì)算（一）單元教學(xué)設(shè)計(jì)1. 教案計(jì)劃表單元名稱第十章 壓桿穩(wěn)定學(xué)時1項(xiàng)目名稱第四節(jié) 壓桿的穩(wěn)定計(jì)算（一）教學(xué)地點(diǎn)多媒體教室學(xué)生角色設(shè)計(jì)輔助人員教學(xué)目標(biāo)知識目標(biāo)技能目標(biāo)態(tài)度目標(biāo)（1）了解壓桿穩(wěn)定條件；（2）理解折減系數(shù)法和安全系數(shù)法；（1）能夠說明壓桿穩(wěn)定的條件；（2）能夠熟練掌握安全系數(shù)法和折減系數(shù)法；并能夠準(zhǔn)確查找和確定安全系數(shù)和折減系數(shù)；（1）做好課前預(yù)習(xí)、課后復(fù)習(xí)；（2）能夠按時上課，遵守課堂紀(jì)律，積極回答課堂問題，實(shí)現(xiàn)有效的互動和交流；（3）課下同學(xué)間能對疑難問題相互討論，能認(rèn)真完成老師布置的各項(xiàng)任務(wù)，按時上交作業(yè)。（4）注重提出、分析、

2、解決問題此邏輯思維能力的培養(yǎng)；（5）能勇于表達(dá)個人的觀點(diǎn)和見解。能力訓(xùn)練任務(wù)及案例由許用應(yīng)力的概念引出壓桿穩(wěn)定條件，并說明壓桿穩(wěn)定條件的折減系數(shù)法和安全系數(shù)。教學(xué)重點(diǎn)、難點(diǎn)重點(diǎn)：壓桿穩(wěn)定條件，折減系數(shù)法，安全系數(shù)法。難點(diǎn)：折減系數(shù)法。教學(xué)方法、手段案例法，講練結(jié)合法，黑板、多媒體課件，動畫。教學(xué)組織過程 （1）復(fù)習(xí)回顧：壓桿臨界應(yīng)力的計(jì)算方法和許用應(yīng)力的概念。（2）引入案例：壓桿穩(wěn)定的條件，說明折減系數(shù)法。（3）提出問題：壓桿穩(wěn)定的條件，折減系數(shù)法的原理。（4）教師輔導(dǎo)評價；教師進(jìn)行全過程答疑，觀察學(xué)生的完成的質(zhì)量，根據(jù)邏輯的完整性進(jìn)行評價。（5）最后總結(jié)：闡明在計(jì)算過程中出現(xiàn)的系列問題和注意

3、事項(xiàng)，進(jìn)一步完善解決問題的方法。教學(xué)條件多媒體教學(xué)課件和配套設(shè)備，課程相關(guān)資料。作 業(yè)基礎(chǔ)試題（填空題、簡答題等）備 注2. 教學(xué)實(shí)施【步驟l】復(fù)習(xí)鞏固和引入新課教學(xué)地點(diǎn)教師任務(wù)學(xué)生任務(wù)教學(xué)條件時間（分鐘）多媒體教室學(xué)習(xí)任務(wù)引入與教師互動回答多媒體課件5【步驟2】課程介紹及知識講授教學(xué)地點(diǎn)教師任務(wù)學(xué)生任務(wù)教學(xué)條件時間（分鐘）多媒體教室講解本章的幾個知識點(diǎn)聽課，獲取有關(guān)知識和信息多媒體課件25教學(xué)內(nèi)容及要求：1壓桿穩(wěn)定條件在工程中，為了保證壓桿在軸向壓力作用下不致失穩(wěn)，必須使其橫截面上的工作應(yīng)力滿足下述條件： （10-14）式中：為壓桿的工作應(yīng)力；為穩(wěn)定容許應(yīng)力；為穩(wěn)定安全系數(shù)。在選擇穩(wěn)定安全系

4、數(shù)時，除應(yīng)遵循確定強(qiáng)度安全系數(shù)的一般原則外，還應(yīng)考慮加載偏心與壓桿原本存在彎曲現(xiàn)象等不利因素。因此，穩(wěn)定安全系數(shù)一般大于強(qiáng)度安全系數(shù)。其值可從有關(guān)設(shè)計(jì)規(guī)范中查得。對于金屬結(jié)構(gòu)中的壓桿，穩(wěn)定安全系數(shù)一般取1.83.0。2折減系數(shù)法為了計(jì)算上的方便，在工程實(shí)際中，常采用折減系數(shù)法進(jìn)行穩(wěn)定計(jì)算。將穩(wěn)定容許應(yīng)力值寫成下列形式，則穩(wěn)定條件為 或 式中：為強(qiáng)度計(jì)算時的容許壓應(yīng)力；為壓桿軸力；A為壓桿橫截面的面積，截面的局部削弱對整體剛度的影響甚微，因而不考慮面積的局部削弱，但要對削弱處進(jìn)行強(qiáng)度驗(yàn)算；是一個小于1的系數(shù)，稱為穩(wěn)定系數(shù)或折減系數(shù)。因?yàn)榕R界應(yīng)力和穩(wěn)定安全因數(shù)總是隨柔度的改變而改變，故穩(wěn)定系數(shù)與壓

5、桿的柔度、所用材料、截面類型等有關(guān)，其值可從有關(guān)設(shè)計(jì)規(guī)范中查得。在鋼結(jié)構(gòu)設(shè)計(jì)規(guī)范（GB50017-2003）中，根據(jù)工程中常用構(gòu)件的截面形式、尺寸和加工條件等因素，把截面歸并為a、b、c、d四類，表10-2、表10-3僅列出了三類。表10-4、表10-5、表10-6給出了 鋼對應(yīng)a、b、c三類截面在不同柔度下的值。在木結(jié)構(gòu)設(shè)計(jì)規(guī)范（GB5005-2003）中，按樹種的強(qiáng)度等級分別給出的兩組計(jì)算公式，如下所示：（1）樹種強(qiáng)度等級為：TC15、TC17及TB20： （10-15）（2）樹種強(qiáng)度等級為：TC11、TC13、TB11、TB13、TB15及TB17： （10-16）表10-2 軸心受壓構(gòu)

6、件的截面分類(板厚)截面形式對x軸對y軸 軋制a類a類 軋制，a類b類軋制，焊接，翼緣為焰切邊焊接b類b類軋制軋制等邊角鋼軋制，焊接(板件寬厚比20)軋制或焊接b類b類焊接軋制截面和翼緣為焰切邊的焊接截面b類b類格構(gòu)式焊接，板件邊緣焰切焊接，翼緣為軋制或剪切邊b類c類焊接，板件邊緣為軋制或剪切焊接，板件寬厚比20c類c類表10-3 心受壓構(gòu)件的截面分類(板厚)截面形式對x軸對y軸 軋制工字形或H形截面b類c類軋制工字形或H形截面c類d類焊接工字形截面翼緣為焰切邊b類b類翼緣為軋制或剪切邊c類d類焊接箱形截面板件寬厚比20b類b類板件寬厚比20c類c類表10-4 鋼a類截面軸心受壓構(gòu)件穩(wěn)定系數(shù)0

7、12345678901020304050607080901001101201301401501601701801902002102202302402501.0000.9950.9810.9630.9410.9160.8830.8390.7830.7140.6380.5630.4940.4340.3830.3390.3020.2700.2430.2200.1990.1820.1660.1530.1410.1301.0000.9940.9790.9610.9390.9130.8790.8340.7760.7060.6300.5550.4880.4290.3780.3350.2980.2670.24

8、10.2180.1980.1800.1650.1520.140-1.0000.9930.9770.9590.9370.9100.8750.8290.7700.6990.6220.5480.4810.4230.3730.3310.2950.2640.2380.2150.1960.1790.1640.1500.139-1.0000.9920.9760.9570.9340.9070.8710.8240.7630.6910.6150.5410.4750.4180.3690.3270.2920.2620.2360.2130.1940.1770.1620.1490.138-0.9990.9910.9740

9、.9550.9320.9040.8670.8180.7570.6840.6070.5340.4690.4120.3640.3230.2890.2590.2330.2110.1920.1750.1610.1480.136-0.9990.9890.9720.9520.9290.9000.8630.8130.7500.6760.6000.5270.4630.4070.3600.3200.2850.2560.2310.2090.1900.1740.1590.1470.135-0.9980.9880.9700.9500.9270.8970.8580.8070.7430.6680.5920.5200.45

10、70.4020.3560.3160.2820.2530.2290.2070.1890.1720.1580.1460.134-0.9980.9860.9680.9480.9240.8940.8540.8010.7360.6610.5850.5140.4510.3970.3510.3120.2790.2510.2260.2050.1870.1710.1570.1440.133-0.9970.9850.9660.9460.9210.8900.8490.7950.7280.6530.5770.5070.4450.3920.3470.3090.2760.2480.2240.2030.1850.1690.

11、1550.1430.132-0.9960.9830.9640.9440.9190.8860.8440.7890.7210.6450.5700.5000.4400.3870.3430.3050.2730.2460.2220.2010.1830.1680.1540.1420.131-表10-5 鋼a類截面軸心受壓構(gòu)件穩(wěn)定系數(shù)012345678901020304050607080901001101201301401501601701801902002102202302402501.0000.9920.9700.9360.8990.8560.8070.7510.6880.6210.5550.4930.

12、4370.3870.3450.3080.2760.2490.2250.2040.1860.1700.1560.1440.1330.1231.0000.9910.9670.9320.8950.8520.8020.7450.6810.6140.5490.4870.4320.3830.3410.3040.2730.2460.2230.2020.1840.1690.1550.1430.132-1.0000.9890.9630.9290.8910.8470.7970.7390.6750.6080.5420.4810.4260.3780.3370.3010.2700.2440.2200.2000.1830

13、.1670.1540.1420.131-0.9990.9870.9600.9250.8870.8420.7910.7320.6680.6010.5360.4750.4210.3740.3330.2980.2670.2410.2180.1980.1810.1660.1530.1410.130-0.9990.9850.9570.9220.8820.8380.7860.7260.6610.5940.5290.4700.4160.3700.3290.2950.2650.2390.2160.1970.1800.1650.1510.1400.129-0.9980.9830.9530.9180.8780.8

14、330.7800.7200.6550.5880.5230.4640.4110.3650.3260.2910.2620.2360.2140.1950.1780.1630.1500.1380.128-0.9970.9810.9500.9140.8740.8280.7740.7140.6480.5810.5170.4580.4060.3610.3220.2880.2590.2340.2120.1930.1760.1620.1490.1370.127-0.9960.9780.9460.9100.8700.8230.7690.7070.6410.5750.5110.4530.4020.3570.3180

15、.2850.2560.2320.2100.1910.1750.1600.1480.1360.126-0.9950.9760.9430.9060.8650.8180.7630.7010.6350.5680.5050.4470.3970.3530.3150.2820.2540.2290.2080.1900.1730.1590.1460.1350.125-0.9940.9730.9390.9030.8610.8130.7570.6940.6280.5610.4990.4420.3920.3490.3110.2790.2510.2270.2060.1880.1720.1580.1450.1340.12

16、4-表10-6 鋼a類截面軸心受壓構(gòu)件穩(wěn)定系數(shù)012345678901020304050607080901001101201301401501601701801902002102202302402501.0000.9920.9660.9020.8390.7750.7090.6430.5780.5170.4630.4190.3790.3420.3090.2800.2540.2300.2100.1920.1760.1620.1500.1380.1280.1191.0000.9900.9590.8960.8330.7680.7020.6360.5720.5110.4580.4150.3750.339

17、0.3060.2770.2510.2280.2080.1900.1750.1610.1480.1370.127-1.0000.9880.9530.8900.8260.7620.6950.6290.5660.5050.4540.4110.3710.3350.3030.2740.2490.2260.2060.1890.1730.1590.1470.1360.126-0.9990.9860.9470.8840.8200.7550.6890.6230.5590.5000.4490.4070.3670.3320.3000.2710.2460.2240.2050.1870.1720.1580.1460.1

18、350.125-0.9990.9830.9400.8770.8140.7480.6820.6160.5530.4940.4450.4030.3640.3280.2970.2690.2440.2220.2030.1860.1700.1570.1450.1340.124-0.9980.9810.9340.8710.8070.7420.6760.6100.5470.4880.4410.3990.3600.3250.2940.2660.2420.2200.2010.1840.1690.1560.1440.1330.124-0.9970.9780.9280.8650.8010.7350.6690.6040.5410.4830.4360.3950.3560.3220.2910.2640.2390.2180.1990.1280.1680.1540.1430.1320.123-0.9960.9760.9210.8580.7940.7290.6620.5970.5350.4770.4320.3910.3530.