 SkyCiv文档

1. 教育
2. 示范课程
3. AISC钢桥比赛

# AISC钢桥比赛

## AISC学生钢桥比赛桥梁结构分析设计能力介绍

SkyCiv Structural 3D 为学生提供了分析能力和适应性的完美结合. SkyCiv 以缩短学习软件和有效操作软件所需的时间而自豪, 导致更多时间 增值 到他们的项目, 而且很快.

### 桁架结构建模

Using the bridge envelope constraint documents provided by AISC in the AISC Student Steel Bridge – 2019 规则, 我们观察到以下: (资源: AISC学生钢桥比赛 2019 规则)

We will use a Pratt Truss for our example. 单击链接以获取有关的更多信息 Truss TypesModeling a Truss. We are going to analyze the stringers as a single member to simplify our model at this stage. More complex stringers can easily be modeled as students move forward in the design process.

Looking at the bridge section, we will assume that ground level is the Y-elevation of 0, and our stringer’s centroid passes through a Y-elevation of 1 脚. Looking at the side elevation, lets assume our supports are centered at each of the 1′-0″ wide footing locations. This would give us a bottom stringer length of 22 脚. For the top stringer of our bridge truss, lets say that its centroid passes through the Y-elevation of 4.75 英尺. 最后, we will assume that there are six equal spaces between the ends of our bottom stringers, so our truss connection location spacing is 22 ft/6 = 3.67 英尺.

Now that we have the general dimensions our bridge envelope, lets create the nodes. Here’s our node table, with the X-direction being the long dimension for the truss and the Y-direction being the elevation.  Now lets add some supports. Taking another look at the AISC Bridge Envelope drawing, the right footing is located inward from the end of the bridge, creating a cantilever. To accommodate this, lets move Node 6 and Node 8 to line up with the location of this support; The center of the footing is 3′-0″ inward from the right ride, so our X-dimension will be 19 脚. 最后, lets add pin supports at N0de 1 and Node 8. Take a look at our updated truss:   Modeling in SkyCiv’s Structural 3D module is extremely intuitive and leads to quicker analysis and simpler results. Give your students a try modeling a truss in 2D using our Free Truss Calculator tool.

### Applying Loads to our Bridge

After modeling, now we can start to apply the loads set by AISC. There are two load types of loads, or load cases, that the bridge will be tested on: Lateral and Vertical. The magnitudes of each load case are given by AISC, but their exact location along the bridge length is not. 因此, students will need to analyze multiple different locations for each load case to find out the worst case scenario for each. It should be noted that each load case is applied independently; the structure does not see both loading situations at the same time.

Because the loads that are supplied by AISC are ACTUAL loads that will be used in the competition, we can assume they are service loads. We are trying to design this bridge the lightest we can while still meeting the deflection criteria. 因此, our Load Combinations will not include any amplifying load factors.

For the Lateral Load Case, lets look at the load drawing supplied by AISC in the 2019 规则 (数字 2): (资源: AISC学生钢桥比赛 2019 规则) $$Lateral\:Load = 50\:lb = 0.05\:kip$$

$$Vertical\:Load=75\:lb/3\:英尺= 25\:lb/ft = 0.025\:kip/ft$$

$$LC\:1=1.0*Self\:Weight\:of\:结构体 + 1.0*Lateral\:Load\:Case$$ For the Vertical Load Case, lets look at the load drawing supplied by AISC in the 2019 规则 (数字 2): (资源: AISC学生钢桥比赛 2019 规则)

The pre-loading will be its own load case and will be calledVertical Load CasePre-load”. Lets apply the distributed loads centered at Node 21/9 and Node 24/12. 节点 24 和 12 are mirrored across the center of the bridge.

$$Preload = (100\:lb/2)/3\:英尺= 16.7\:lb/ft = 0.0167\:lb/ft$$

$$LC\:2=1.0*Self\:Weight\:of\:结构体 + 1.0*Vertical\:Load\:Case-Preload$$ $$Total\:Load\:on\:Left\:Side\: = (1500\:lb/2)/3\:英尺= 250\:lb/ft = 0.25\:kip/ft$$

$$Total\:Load\:on\:Right\:Side\: = (1000\:lb/2)/3\:英尺= 167\:lb/ft = 0.167\:kip/ft$$

Our last load combination is therefore identified as:

$$LC\:3=1.0*Self\:Weight\:of\:结构体 + 1.0*Vertical\:Load\:Total$$

Here is what our model looks like with the total load applied in the vertical load case: See the below for a picture of a recent competition and the loading mechanism for the vertical load case: The last portion of this exercise is running the analysis on our bridge structure and interpreting the results. Before we do that, lets take a look at the load combinations and their load factors: These loads are service loads, so we will be using a load factor of 1.0 on all of them. These three load combinations encapsulate the loading conditions presented between the Lateral Load Case and Vertical Load Case, provided by AISC. 现在, lets run our analysis. 出于实际目的, we will look at the axial results for the right truss with the cantilevered end for LC 3. SkyCiv gives the users power to hide, isolate and view their structures results in whatever way they see fit. Look at the entire structure for a more global idea, or isolate combinations or single members to evaluate on a more granular level. 从这里, students will need to go through the iterative design and collaboration process with their team. Students can now focus on becoming better and well-prepared engineers for not only the AISC Student Steel Bridge competition, but as an Engineer-in-Training and Professional Engineer.

This example shows how powerful yet simple SkyCiv 3D can be, with its intuitive modules aimed towards users ranging from first year engineering students to principal engineers at the height of their careers. SkyCiv hopes that it can be a prominent tool for use within the classroom, allowing students to focus on learning about engineering rather than learning about the software.

## 参考资料:

• “University Programs.” 学会, 2019, www.aisc.org/education/university-programs/student-steel-bridge-competition/.