[學(xué)士]四層框架結(jié)構(gòu)中學(xué)實驗樓畢業(yè)設(shè)計（含建筑圖 結(jié)構(gòu)圖 計算書）
[學(xué)士]四層框架結(jié)構(gòu)中學(xué)實驗樓畢業(yè)設(shè)計（含建筑圖 結(jié)構(gòu)圖 計算書）,學(xué)士,[學(xué)士]四層框架結(jié)構(gòu)中學(xué)實驗樓畢業(yè)設(shè)計（含建筑圖,結(jié)構(gòu)圖,計算書）,框架結(jié)構(gòu),中學(xué),實驗,畢業(yè)設(shè)計,建筑,計算
唐 山 學(xué) 院 畢 業(yè) 設(shè) 計
Static lateral force procedure for buildings
2.1 DETERMINATION 0F LATERAL FORCES
2.1.1 Seismic zone factor
The seismic zone factor Z，given in UBC Table 16—1，is the Code estimate of the applicable site dependent effective peak ground acceleration expressed as a function of the gravity constant g·.The values of Z range from 0．075 to O．40 with the USA being divided into six different seismic zones in UBC Figure 16—2．
The zone factor corresponds to ground motion values with a recurrence interval of 475 years which gives a ten percent probability of being exceeded in a riftv year period．These values are based on historical records and geological data and are also adjusted in order to provide consistent design criteria within local jurisdictions．The zone factor is used，in conjunction with the soil profile type，to determine the appropriate ground response coefficients Ca and Cv。given in UBC Tables 16-Q and 16一R．These are then used tO provide the response spectrum envelope illustrated in UBC Figure 1 6-3．
2.1.2 Ground response coefficients
The ground response coefficients C。and C。are defined in UBC Section 1629．4．3 and are parameters which reflect the potential amplification of the ground vibration caused by different soil types．These coefficients are a function of the zone factor Z，the soil profiles SA tO SF and，where applicable，the near—source factors Na and N。．The fundamental period of a structure determines which of the two coefficients Ca or Cv governs the seismic design of the structure．The acceleration—based coefficient Ca controls for shorter periods up to approximately one second and the velocity—based coefficient C。controls for longer periods．Values of C。and C、are given in Table 2—1 for soil profiles type A to type E．A site—specific geotechnical investigation is necessary to determine the value of the coefficients for soil profile type F．
2.1.3soil profile types
The ground vibration caused by an earthquake tends to be greater on soft soil than on hard soil or rock．As the vibration propagates through the material underlying the structure，it may be either amplified or attenuated depending on the fundamental period of the material．To account for this potential amplification，six different soil types are identified in the Code ranging from hard rock to soft soil．The classification may be made by determining on site the average shear Wave velocity in the top 100 feet of material．Alternatively，for soil profile types C，D，or E，the classification may be made by measuring the standard penetration resistance or undrained shear strength of the material．For rock and hard rock，the shear wave velocity may be estimated by comparison with measurements taken on rock of similar composition．Soil profile type SB is described as rock and is that material in which the ground response coefficients C。and CV are identical to the effective peak acceleration value Z．Soil profile type SB Occurs mainly in the western states．Soil profile type SA is described as hard rock and has the effect of reducing the ground response coefficients by 20 percent．Soil profile type SA occurs mainly in the eastern states．Soil profile type SE is described as soft soil and has the effect of increasing the velocity—based ground response coefficient Cv by up to 230 percent．For soil profile type SF，which is described as sensitive clay or peat vulnerable to potential failure，a site specific hazard evaluation is required to determine the ground response coefficients.When soil parameters are unknown，in accordance with UBC Section 1629．3，soil profile type SD may be assumed unless it is determined that soil profile types SE or SF may be present at the site．Table 2-2 lists the soil profile types．
2.1.4 Seismic source classification
The maximum moment magnitude potential of a fault and its slip rate are used to classify seismic source types. Five different source types are identified in the Code ranging from the most active type A source to the least active type C source. Type C sources are relatively" inactive faults, not capable of producing large magnitude earthquakes, and occur mostly outside California. Table 2-3 lists the different types of faults.
2.1.5 Near source factor
In regions subjected to large magnitude earthquakes, such as those which occur in seismic zone4, locations close to the fault rupture may experience a ground acceleration up to twice that at a distance of 10 kilometers from the source. To account for this, the Code introduces two near-source amplification factors. These are Na the acceleration-based factor for short period structures and Nv the velocity-based factor for periods exceeding one second. These factors are applicable to seismic source type A and seismic source type B, and have a value of unity for type C faults regardless of distance.
2.1.6 Fundamental period
Each structure has a unique natural or fundamental period of vibration which is the time required for one cycle of free vibration. The factors determining the fundamental period include the stiffness and height of the structure, and the fundamental period may vary from 0.1 seconds for a single-story building to several seconds for a multi-story building. As a first approximation, the fundamental period may be assumed equal to the number of stories divided by l0.
2.1.1 1 Seismic response coefficient
The seismic response coefficient Cs given in the NEHRP Recommended Provisions30,31,32 is used
to represent the design elastic acceleration response of a structure to the input ground motion．The corresponding expression may be derived from UBC Formula(30—4)as
Cs =Cv I／RT
where I =importance factor，for a specific occupancy category，from UBC Table 16-K
Cv =velocity—based ground response coefficient，for a specific seismic zone
and soil profile，from UBC Table 16-R
R =response modification factor，for a specific structural system，from UBC
Table 16-N
T =fundamental period of vibration，from UBC Formula(30—8)or(30—1 0)
The form of this expression indicates that the response coefficient increases as the importance factor increases and the response modification factor and natural period reduce．
The value of the response modification factor is determined from consideration of a structure’s overstrength capacity beyond the point at which the elastic response of the structure is exceeded．
The value of the response modification factor always exceeds unity，which indicates that all structures are designed for forces less than would be produced in a completely elastic structure．This reduced force level is made possible by the energy absorption and dissipation capacity of the structure at displacements in excess of initial yield．Lightly damped structures constructed of brittle materials are unable to tolerate appreciable deformation in excess of initial yield and are assigned low values of R．Highly damped structures constructed of ductile materials are assigned larger values of R．The effect of the importance factor is to increase the seismic response coefficient by 25 percent for essential facilities and hazardous facilities．This raises the seismic level at which elastic response is exceeded and the operational capacity of the structure is impaired．For fundamental periods in excess of approximately one second，the acceleration response of a structure attenuates proportionally to its period and this is reflected in the form of the expression for the seismic response coefficient．
The maximum value of the seismic response coefficient may be derived from UBC Formula(30—5) as
Cs ≤2．5C。I／R
where Ca =acceleration-based ground response coefficient，for a specific seismic
zone and soil profile，from UBC Table 16-Q
This expression controls for shorter periods up to approximately one second． For longer periods，the expression provides conservative values．To prevent too low a value of the seismic response coefficient being adopted for long period structures，the minimum permitted value is given by UBC Formula(30-6)as
Cs≥0.1 lCaI
In seismic zone 4，at locations less than 15 kilometers from a potential source，the minimum
value is further modified by UBC Formula(30—7)to
Cs ≥0．8ZNvI／R
where Z =seismic zone factor from UBC Table 16-I
and Nv =velocity—based near source factor from UBC Table 16-T
Example 2-2(Determination of seismic response coefficient一
A three story，steel，moment—resisting frame with the properties shown in Figure 2—2,a height of 36 feet，and with a damping ratio of five percent is located on a site in zone 3 with an undetermined soil profile．Calculate the value of the seismic force coefficient Cs．
Solution
From Table 2-l，using soil profile type SD for the undetermined soil profile，the ground response coefficients are obtained as
Ca =0.36
Cv =0.54
The minimum permitted value of the seismic response coefficient is given by UBC Formula (30-6) as
Cs =0.1 1CaI
=0.11×1.0 X 0.36
=0.040
The value of the response modification factor，for a moment—resisting frame，is obtained from Table 2—6 as
R =8.5
The natural period，using method A．was derived in Example 2—1 as
TA =0.51 seconds
The seismic response coefficient is given by
Cs =Cv I／RT
=1.00×0.54／(8.5× 0.511)
=0.125
The maximum value of the seismic response coefficient is given by
Cs =2.5C。I／R
=2.5×1.0×0.36／8.5
=0.106…governs
The natural period，using method B and after imposing the limitation of UBC Section 1630．2.2，was derived in Example 2—1 as
TA =0.71 seconds
The corresponding seismic response coefficient is given by
Cs =Cv I／RT
=1.00 x 0.54／(8.5×0.71)
=0.090…governs
2．1．12 Seismic dead load
The seismic dead load W as specified in UBC Section I 630．1．1, is the total dead load of the structure and that part of the service load which may be expected to be attached to the building．
This consists of
● Twenty—five percent of the floor live load for storage and warehouse occupancies．
● A minimum allowance of ten pounds per square foot for moveable partitions．
● Snow loads exceeding thirty pounds per square foot．which may be reduced by seventy——five percent depending on the roof configuration and anticipated ice buildup．
● The total weight of permanent equipment and fittings．
Roof and floor live loads，except as noted above，are not included in the value of W as they are considered negligible by comparison with the dead loads．In designing floor members for gravity loads，the loading intensity specified in UBC Section 1606．2 for moveable partitions is twenty pounds per square foot．This value allows for local concentrations of the partitions，while the overall average value of ten pounds per square foot is adopted for seismic loads．For permanent walls which are constructed of heavier materials，the actual weight of the walls shall be used．Freshly fallen snow，not exceeding thirty pounds per square foot，has little effect on the seismic load as it tends to be shaken off the roof in the initial phase of an earthquake．However ice and compacted snow，exceeding thirty pounds per square foot，may be expected to adhere to the roof and contribute fully to the seismic load．
建筑靜態(tài)水平力分析
2.1水平力決定因素
2.1.1地震帶因素
在UBC表16-1種給出的，地震帶Z因素是估計規(guī)范的可應(yīng)用場地，它取決于有效的地面加速度峰值即重力加速度g。z值的取值范圍為0.075-0.40，據(jù)此美國在UBC 16-2中劃分為六個不同的地震區(qū)。地震區(qū)與以475年為周期的地面運動值相符合，并在50年內(nèi)有10%的可能超過它。這些值是是在歷史記載、地質(zhì)資料的基礎(chǔ)上確定的，并且為了在地方容許的范圍內(nèi)提供設(shè)計標(biāo)準(zhǔn)的做了調(diào)整。區(qū)域因素與土層特性共同決定了場地影響系數(shù)Ca、Cv，見UBC表16-Q和16-R。這些后來用做反映譜包絡(luò)，見UBC16-3圖解。
2.1.2場地影響系數(shù)
場地影響系數(shù)Ca、Cv是在UBC1629.4.3部分中定義，而且反映了由不同的土壤類型引起的地面震動參數(shù)潛在的擴大。這些系數(shù)是Z因素、土層Sa-Sf和近源因素Na、Nv的函數(shù)。建筑的基本周期決定結(jié)構(gòu)Ca或Cv系數(shù)，系數(shù)Ca控制大約到一秒的短周期，系數(shù)Cv則控制較長周期。A類型土層到E類型土層的Ca和Cv的值見表2-1。對于一個場地特殊的土質(zhì)調(diào)查研究是必須的，這可以決定對于土層的F系數(shù)。
2.1.3土層類型
由地震引起的地面震動在軟土上要比在硬土或巖石上強。隨著震動的傳播通過底層結(jié)構(gòu)的材料，它也許會增強 也許會削弱，這由材料的基本周期決定。為了說明這種潛在的影響，規(guī)定中從硬土到軟土定義了六種不同的土壤類型。這種分類等級可能是由場地在最深100英尺的土層中的剪切波的速度決定的。另外，對于土壤剖面類型C，D或E的分類也許是根據(jù)材料標(biāo)準(zhǔn)的抗?jié)B力或不排水固結(jié)強度。對于巖石或堅硬的土壤，剪切波速也可通過與從相似成分的巖石測量值來估計,SB類型土壤剖面被描述為石頭，SB類型是場地影響系數(shù)Ca和Cv都能有效地達到Z加速度峰值的材料。SB類型土壤大部分在西部。SA類型土壤剖面是堅硬巖石，能夠有效地降低場地影響系數(shù)的20%。SA類型土壤大部分在西部。SE類型土壤別稱為軟土，能夠有效地增加波速，基于場地影響系數(shù)Cv 提升230%，SF類型土壤被描述成一種敏感的粘土或者易變形的泥土，對這種場地一個特殊的危害評價來確定場地的影響系數(shù)。當(dāng)土壤的參數(shù)未知道時，與UBC 1629.3一致，SD類型土壤可以估定除非SE類型土壤或SF類型土壤出現(xiàn)在場地中。
2.1.4地震源等級
最大限度瞬間潛在的震源和它的滑動率被用來劃分地震源類型。規(guī)范從最活躍的A類型到最不活躍的C類型定義為五個不同的震源類型。C類型與不活躍的震源有關(guān)，不能夠產(chǎn)生巨大的地震，大多數(shù)經(jīng)常發(fā)生在加利福尼亞的外圍。表2-3 列出不同類型的地震。
2.1.5近源因素
在經(jīng)常發(fā)生大型地震的區(qū)域，比如在4地震帶靠近斷層破裂的地方，在距離震源10千米外擴展速度能提高到兩倍。為了說明這些，規(guī)范介紹了兩種近源擴大因素。這些是Na加速度基礎(chǔ)因素短周期的結(jié)構(gòu)和Nv速度因素超過一秒的結(jié)構(gòu)。這些因素應(yīng)用于震源為A類型和B類型，和一個聯(lián)合值應(yīng)用于C類型的與距離無關(guān)。Na和Nv的值在表2.4中給出。
2.1.6自振周期
每一種建筑結(jié)構(gòu)都有它固有的振動周期或自振周期，即一次自由振動所需要的時間。決定結(jié)構(gòu)自振周期的因素有結(jié)構(gòu)的剛度和高度。自振周期的值大約在0.1s（對單質(zhì)點體系）與幾秒（對多質(zhì)點體系）之間，也可近似的取為建筑層數(shù)的0.1倍。
2.1.11地震反應(yīng)系數(shù)
在NEHRP推薦的版本中給出的地震反應(yīng)系數(shù)用來表明彈性設(shè)計對結(jié)構(gòu)在地震運動中的加速反應(yīng).符合上述表述的公式UBC30-4,如下:
其中: I:重要因素,與場地類型有關(guān)見表UBC 16-K；
Cv:地震反應(yīng)速率系數(shù),與地震帶和地基土有關(guān)見表16-R；
R:地震反應(yīng)限制因素,與結(jié)構(gòu)體系本身有關(guān).見表UBC16-N；
T:自震基本周期,見UBC公式(30-8)或(30-10)。
以上公式表明地震反應(yīng)系數(shù)隨著I(重要因素)的增加,R(地震反應(yīng)限制因素)和T(自震基本周期)的降低而增加。
地震反應(yīng)限制因素的價值是由考慮結(jié)構(gòu)通過超出彈性反應(yīng)的那部分承載能力所決定的。
地震反應(yīng)限制因素的值總是超出結(jié)構(gòu)整體,這表明所有的結(jié)構(gòu)都將按低于僅按彈性設(shè)計的承載力進行設(shè)計。設(shè)計承載力的減少很可能是由于建筑結(jié)構(gòu)地震時發(fā)生超出最初位置的位移產(chǎn)生吸收和消散地震能而造成的。構(gòu)成輕質(zhì)阻尼結(jié)構(gòu)的脆性材料不能承受超出最初位移的適當(dāng)變形,因此被設(shè)定為降低了R(地震反應(yīng)限制因素)的值。構(gòu)成高層阻尼結(jié)構(gòu)的延性性材料被設(shè)定為增大了R(地震反應(yīng)限制因素)的值。重要因素所產(chǎn)生的影響可將重要設(shè)施和有危險的設(shè)施的地震反應(yīng)系數(shù)提高25%。隨著地震反應(yīng)的彈性設(shè)計水平提高,建筑結(jié)構(gòu)的工作能力被削弱了。
對于那些基本周期超出一秒的場地,從周期來看對稱結(jié)構(gòu)會加速地震反應(yīng),這可從地震反應(yīng)系數(shù)的表達式可反應(yīng)出。
地震反應(yīng)系數(shù)的最大值可由
得出,如下:
Cs≤2.5CaI/R
Ca=場地加速度反應(yīng)系數(shù),與地震區(qū)劃和地基土有關(guān)。見UBC表16-Q.
以上表達式僅適用于周期低于1s的建筑而言,對于更長的周期,表達式給出了保守值。
為使長周期結(jié)構(gòu)的地震反應(yīng)系數(shù)不至于太低, 公式UBC(30-6)給出了Cs的最小值。
如下:
Cs≥0.11 CaI
在地震區(qū)劃4中,距離震源少于15Km的位置, 地震反應(yīng)系數(shù)的最小值被進一步修改,見公式UBC(30-7)T:
Cs≥0.82NVI/R
Z:地震反應(yīng)因素。見UBC表16-I
NV:震源附近的波速。見UBC表16-T。
例2-2:(確定地震反應(yīng)系數(shù))
又一個例子:一鋼框架建筑抵抗瞬間地震反應(yīng)見表2-2,高36尺,阻尼比為5%,場地為第三區(qū)劃,地基土為不確定的簡單土質(zhì)。計算地震反應(yīng)系數(shù)的值Cs。
答案: 由表2-1得:用SD型土代替題目中并不確定的土壤類型,則場地反應(yīng)系數(shù)可得:
Ca=0.36, Cv=0.54
由公式UBC(30-6)給出的地震反應(yīng)系數(shù)允許最小值:
Cs=0.11 CaI
=0.11×1.0×0.36
=0.040
對于一個受瞬間地震作用的框架而言, 地震反應(yīng)限制因素的值可由表2-1得: R=0.85。
自震周期,用方法A可由例2-1得到如下:TA=0.51秒。
地震反應(yīng)系數(shù)可按下式得到: Cs=2.5CaI/R=2.5×1.0×3.6/0.85
=0.106 滿足要求
自震周期,自遭受UBC1630.22部分限制后可由方法B由例2-1得出如下:
TA=0.71秒.。
與題意相符的地震反應(yīng)系數(shù)可由下式得出:
Cs= Cv I/RT
=1.00×0.54/(8.5×0.71)
=0.090 滿足要求
2.1.12地震恒載
在UBC1630.1.1版本中給出的地震恒載W是指整個建筑結(jié)構(gòu)恒載以及需要安裝在建筑物上的設(shè)備荷載之和。
其組成如下：
● 25%的倉庫營業(yè)期間的樓面活載。
● 可動設(shè)備每平方英尺十磅重最小限額。
● 每平方英尺超出30英鎊的雪荷載，或許能通過考慮樓層構(gòu)造和預(yù)想的冰載減少75%。
● 永久設(shè)備的總重。
除了以上所提到的，樓面和屋面活載沒被包含在W（重量）的值中，因為相比恒載而言它們可以忽略不計?？紤]重力荷載而設(shè)計的樓層構(gòu)件，荷載極限值按UBC1606.2版可動設(shè)備確定的值為20磅每平方英尺。這個值考慮到隔墻的集中荷載，然而每平方英尺10磅的總平均值是地震荷載所允許的。對于構(gòu)成較重材料的承重墻，墻體的實際重量將被用到。對于剛下落的松散的雪載，當(dāng)荷載值不超過30磅每平方英尺，將對地震荷載幾乎沒影響，因為在地震的最終階段雪將被抖落掉。然而冰和壓實的雪，當(dāng)其荷載值超過30磅每英尺時，將被考慮到附著在樓面上以及產(chǎn)生附加的地震作用。
10
收藏