本文授权转载自公众号同济设计四院
作者：刘冰
PREFACE
随着社会的发展，建筑的造型也更为多元化。总体而言，精致、高耸，大跨，科技感成为当前建筑师挑战的方向。对于大型结构，需要各种抗震或超限审查，经过专家的层层论证，往往具有足够的安全储备，甚至可以抵御罕遇地震的袭击。但对于日渐兴起的小型网红类结构，其造型大胆震撼，体系简洁高效，无冗余度，同时建筑师往往对于结构尺度具有近乎苛刻的要求，因此安全度反而更成为关注点。
With development of society, architectures are more diversified. Generally speaking, exquisite, high-rise, large-span, technology become the current challenge. For large-scale structure, it needs some seismic reviews. After the evaluation of experts, it can resist the attack of rare earthquakes and has enough safety reserves. But for the small structure, its modeling is bold and shocking, the system is simple and efficient, and there is not enough redundancy. At the same time, architects often have strict size requirements,so the safety is the focus.
此类建筑，空间狭小，留给结构发挥的空间极其有限。在满足空间效果的前提下，如何实现结构的安全度、美观度的统一，便成为了结构工程师面临的新挑战。以本文通过近期竣工的深圳茅洲河碧道之环项目为例，阐述如何通过集约型思维，外加科技赋能，将结构的不可能变为可能。
The space of this kind of building is narrow. For the space effect, how to realize the unity of safety and beauty of the structure has become a new challenge.Taking the recently completed project River Ring（Shenzhen） as an example, this paper expounds how to make the structural impossibilitypossible through intensive thinking and technology empowerment.
INTENSIVE THINKING OF STRUCTURE
碧道之环项目位于深圳宝安区茅洲河北一段弯折的河床上。建筑以地景式的消隐状态沿着堤岸蜿蜒展开，通过覆土实现了建筑与自然的融合。顶部设置一个直径30米，悬挑达到14米的漂浮圆环，既可以隔岸远眺，又可以登环俯视，形成了“你站在岸边看风景，看风景人在环上看你”般绝美的意境。在圆环中部，设置一个优美的旋转楼梯，上接圆环，下接地面，宛如翩翩起舞的少女。
River Ring is located on the river bed of Maozhou River, Bao’an District, Shenzhen.The building is in the state of landscape, meandering along the embankment, and realizing the integration of architecture and nature by covering soil. Afloating ring with a diameter of 30m and a cantilever of 14m is set on the top,forming a beautiful artistic conception of “you stand on the shore to see the scenery, and the people look at you on the ring”. In the middle of the circle, there is a revolving staircase, which connects the ring and the ground, just like a dancing girl.
整个结构可分为“一坡、一球、一环、一梯”四部分，其中，分解图如下所示。其中为了满足坡地绿化的固土要求，结构工程师与建筑师做了多种尝试，最终确定了整体砼梁上翻，梁底同板底的方案。这样的好处显而易见，首先使室内的结构顶面是平整的，保证了建筑的净高，实现了外露结构的可能性；其次上翻的砼梁起到了固土格栅的作用，防止坡地土体下滑；至于坡屋面的排水问题，通过在砼梁上打孔来实现。整个结构设计理念兼顾了室内、景观、排水等，体现了一种高度集约式的设计思路。
The whole structure can be divided into four parts: slope, ball, ring and ladder. In order to meet the soil consolidation, structural engineers and architects made some attempts, and finally determined that the whole concrete beam is turned up. The advantages are obvious. Firstly, the top surface of the indoor structure is flat, which ensures the clear height and realizes the exposed structure. Secondly, the upturned beam prevent the slope soil from sliding. As for the drainage, it is realized by drilling holes on beams. The design concept takes into account the interior, landscape, drainage and so on, reflecting a highly intensive design idea.
Structure system split diagram
坡顶的漂浮圆环是整个项目的亮点，其直径30米，只有4个支点，从外边缘到支点的垂直距离为9.6m，但由于外边线为圆弧形，所以其外边缘至支点的实际距离将近14m，属于大悬挑的结构。环的宽度呈渐变状，在左侧悬挑端，其宽度约为2.85米，在右侧悬挑端，其宽度约为1.95米。断面形状是一个非等截面的三角形。
The floating ring on the top of the slope is the highlight. Its diameter is 30 meters, and there are only four fulcrums. The actual distance from the outer edge to the fulcrum is nearly 14m due to the arc shape of the outer edge, which belongs to the large cantilever structure. The width ofthe ring is gradually changing, about 2.85m at the left cantilever end and 1.95m at the right cantilever end. The shape of cross section is a triangle with unequal cross section.
Structural geometric dimensions
结构工程师首先想到的是易于施工的空间管桁架方案，并据此进行了计算，桁架外表的高度约为1.365m，经过与建筑师讨论后发现存在两个问题：
The structural engineer first thought of pipe truss scheme which is easy to construct, and made a preliminary calculation. The height of the truss skin is about 1.365m. After discussion with the architect, two problems were found.
1）整体尺度偏大：管桁架上部需要依次铺设龙骨，底层钢衬板等装饰面层，总厚度达到1.485m，整个圆环显得不够轻盈。
The overall scale is too large: the upper part of the pipe truss needs to lay keel, the bottom steel lining and other decorative surface layer, the total thickness reaches 1.485m, the whole ring is not light enough.
2）整体刚度不足：通过对管桁架的变形进行细致研究，当观景的人群集中在圆环外侧观察河景时，整个管桁架会产生一个外翻的扭转，内外的竖向变形差将达到68mm，虽然不违反规范要求，但显然将给游客带来不舒适的体验，同时过大的翻转变形，也会带来玻璃栏杆的破碎风险。
Lack of overall: through detailed research on the deformation, when the spectators gathers on the outside of the ring, the pipe truss will produce an eversion torsion, and the vertical deformation difference between the inside and outside will reach 68mm. Although it does not violate the specification, it will bring uncomfortable experience to tourists. At the same time, excessive overturning deformation will also bring inconvenience risk of broken glass railings.
Section andoverturning deformation of pipe truss
Three dimensional model of pipe truss
基于以上两点，空间管桁架的方案不是一个最优的方案。通过与建筑师的探讨，发现在这么小尺度的构件里面，还按照常规做法把结构和建筑分成若干层级，各司其职，显然是一种冗余。而其带来的直接坏处就是扩大了建筑的表观尺寸。那为何不采用集约型的做法呢？将建筑所需要的顶层包板、侧面包板直接做成结构钢板，形成双曲板复合三角形截面。这样带来的直接好处就是，由于上下钢板的中心距拉大，同样表观尺寸，结构的抗弯刚度提升了25%，抗扭刚度提升了20%。结构完成面高度直接从1.48m高降低为1.30m高，前面提到的尺度和刚度问题迎刃而解。
Based on the above two points, the scheme of space pipe truss is not an optimal one. Through the discussion with the architect, it is found that in such a small-scale component, the structure and building are divided into several levels, which is obviously a kind of redundancy. And it can expand the apparent size of the building. Why not adopt an intensive approach? The top slab and side slab are directly made into structural steel plate to form double curved plate composite section. The bending stiffness and torsional stiffness of the structure are increased by 25% and 20% due to the larger center distance between the upper and lower steel plates and the same apparent size. The height of the finished surface is directly reduced from 1.48m to 1.30m, so the scale and stiffness problems can be easily solved.
Structural diagram of double curved composite steel plate
但实腹钢板的造型给钢结构的施工带来了难题，由于圆环的断面不断变化，导致三角形的两块侧板形成双曲面钢板，三边焊缝如何能同时严丝合缝的对齐，成为项目的关键。最后，结构工程师创新性的在底部增加了一根D250x25的钢管，上部角部增加了D50圆钢棒，利用钢管较大的焊接面来进行焊缝容错处理，完美解决这一难题。
The solid web steel plate has brought difficulties to the construction. Due to the continuous change of the cross section, the two side form double-curved plate. How to align the three side welds has become the key point. Finally, structural engineers add a d250x25 steel pipe at the bottom and two D50 round steel bars at the upper corner, and use the larger welding surface of the steel pipe to carry out fault tolerance treatment of the weld, which perfectly solves this problem.
TAKE ADVANTAGE OF FORCE
虽然圆环的断面形式得到了最优解，但对于近14米的大悬挑来说，1.3米高的的断面尺寸仍然显得单薄。同时，由于悬挑端与后座跨的长度比达到了2：1，在立柱两侧，圆环弯矩无法平衡，导致立柱本身更需要承担极大的不平衡弯矩。经过计算，立柱需要采用D800的圆管。对于这样一个小型建筑来说，柱子的尺度无法令人接受，而且大小不均的柱子破坏了建筑主立面的序列感和韵律感。
Although the optimal solution is obtained for the cross-section, the cross-section size of 1.3 meters high is still thin for the large cantilever of nearly 14 meters.The length ratio of the cantilever end to the back span reaches 2:1, the bending moment of the rings on both sides of the column can not be balanced, so the column itself needs to bear the great unbalanced bending moment. After calculation, the column needs to use d800 tube, which is obviously unacceptable. It would destroy the sequence and rhythm of the main facade.
Moment distribution of conventional structure
Moment distribution of pre-stressstructure
此时，结构工程师提出一个创新性的想法，在后座跨位置人为增加一个竖向预拉力，增加后座跨在柱子位置的弯矩，使立柱两侧的弯矩达到微妙的平衡。这样柱子类似于杠杆的支点，只承受轴力作用，相应柱子尺寸可减少到D600，与周围常规混凝土柱截面一致，实现了立面上的序列统一。经过多轮试算，发现预拉力在700kN左右，结构平衡性较好。同时，当这个竖向拉力作用到屋面上时，恰好给了屋面一个向上的拉力，平衡了屋面竖向荷载，最终整个结构实现了内力的自我平衡，大幅降低了整个构件尺寸和建造成本，实现了双赢。
At this time, the structural engineer puts forward an innovative idea, which adds a vertical pretension at the back span position to increase the moment of the back span, so that the moment on both sides of the column can reach a balance. In this way, the column only bears the axial force, so its size can be reduced to D600, which is consistent with the surrounding concrete column. After several rounds of calculation, it is found that 700kN is good pretension for the structure. At the same time, when the vertical tension acts on the roof, it just gives the roof an upward tension, balances the vertical load of the roof. Finally it realizes the self balance, and reduce construction cost, and achieves a win-win situation.
Schematic diagram of prestress scheme
对于轻型观景结构来说，解决常规安全性问题只是第一步，对于观景者集中在悬挑端的外侧，集体行走，跑动等特殊荷载，虽然规范并未要求，但作为工程的设计者却必须给与足够重视。经过初步分析，圆环第一阶竖向振动频率为2.5Hz，小于规范要求的3HZ。而且当观景人群位于圆环的最外侧，且有规律的跑动时，其竖向加速度呈喇叭口状的放大趋势，数值放大到2.5m/s2,远远超过《德国人行桥设计指南》所要求的0.5~1.0m/s2的限值，游客的体验感将相当的糟糕。
For the light structure, safety problem is only the first step. The structural engineer also needs to consider the special situation, such as the viewer concentrated on the outside of the cantilever end, walking, running and other special loads. The first vertical vibration frequency of the ring is 2.5hz, which is less than 3Hz required. Moreover, when the spectators are located at the outermost side of the ring and run regularly, their vertical acceleration tends to be amplified to 2.5m/s2, which is far beyond the limit of 0.5 ~ 1.0m/s2 required by the German design guide, and the tourists’ experience will be bad.
Structural vertical model
Half span loading and vertical acceleration time history
因此调谐质量阻尼器（Tuned Mass Damper，后文简称TMD阻尼器）是结构工程师所能想到的解决方案。在两侧大悬挑的端部共设置了5个阻尼器，总质量为3.5吨。
Therefore, tuned mass damper (TMD) is a solution. The engineers set up five dampers at the ends of large overhanging on both sides, with a total mass of 3.5 tons.
人行荷载的随机性导致人致振动反应的随机性，因此人致振动下结构舒适度评价具有复杂性和困难性。由于这类小型结构本身刚度较弱，建筑面层和装饰栏杆等围护结构会对结构刚度产生较大的影响，为了准确评估其舒适度指标，结构团队专门成立科研课题，采用先进的压电式加速度传感仪和振动采集分析仪，对建筑整体完成后的自振频率和阻尼进行实测，调整TMD的阻尼和弹簧刚度，最终进行了人数为10人的同步踏步激励，结果显示器最大加速度约为0.48m/s2，可以满足极端情况下的舒适度要求。最终，TMD的综合减振率可以达到62.5%。
Pedestrian load has a certain randomness, which determines the complexity and difficulty of the comfort evaluation. Moreover, because structure stiffness is weak, its building surface, decorative railings and other enclosure structures will have great impact on the stiffness. In order to accurately evaluate its comfort index, the structure team use advanced piezoelectric acceleration sensor and vibration acquisition analyzer to measure the natural frequency and damping, By adjusting the damping and spring stiffness of TMD, the step excitation of 10 people was carried out. The maximum acceleration of the display is about 0.48m/s2, which can meet the comfort requirements.The comprehensive damping rate can reach 62.5%.
Field test and installation of damper
Time history monitoring of vertical acceleration after TMD installation
REVOLVING STAIRS DESIGN UNDER INTENSIVE CONCEPT
除了顶部的大环以外，建筑师在中间庭院位置增加了一个直径9米，环绕360度的旋转楼梯，大环套小环，交相辉映。旋转楼梯下端接地，上端连接在大环的内悬挑端。初始设计时，结构工程师认为，对于近14米的大悬挑结构来说，承受自身荷载已经勉为其难，为了支撑楼梯，在悬挑端外侧再增100~150kN的竖向力，非常不理性。因此结构工程师提出了增加一根立柱的方案，经过与建筑师的反复讨论，这样破坏了建筑的整体意境。
既然圆环无法给楼梯提供额外的帮助，为何不把楼梯设计成自承重的结构，不给顶部圆环带来额外负担？同时本身扮演一个竖向放置的弹簧作用，当顶部圆环竖向变形过大时，可以给圆环带来一定的支撑作用。
In addition to the big ring, the architect added a 9-meter-diameter, 360 degree revolving staircase in the middle of the courtyard. The lower part of the revolving staircase is grounded, and the upper end is connected with the inner cantilever end of the ring. It was difficult for a large cantilever structure of nearly 14 meters to bear its own load. Now, in order to support the stairs, it is very unreasonable to increase the vertical force of 100~150kN at cantilever end. Therefore, the structural engineer put forward the scheme of adding a column. After discussion with the architect, the overall artistic conception was not accepted. Since the ring can’t provide extra help, why not design the stairs as a self-supporting structure and not bring extra burden to the ring? At the same time, it acts as a vertical spring. When the vertical deformation of the ring is too large, it can bring some support.
Schematic diagram of revolving stairs
如何才能加大旋转楼梯刚度？通常的解决方案就是利用楼梯的栏板作为受力构件，比如杨浦滨江绿之丘的旋转楼梯。但本项目建筑师追求通透的效果，需要采用玻璃栏板，因此需要思考其他的解决方案。传统的旋转楼梯设计时，均采用杆系模型，将两侧梯梁作为杆系单元，中间采用连杆连接，这种做法的优点是结构概念清晰，传力直接，但相应的结构构件尺寸比较大，对于新型的旋转楼梯显得力不从心。因此结构工程师再次想到了“集约型结构”的思路，为何不将楼梯的建筑封板，踏步板统统整合到结构构件中，既可以最少的侵入建筑空间，又可以加快现场施工，减少各类二次面层铺装，更重要的是通过踏步板+底部封板+加劲肋的组合，将两侧的RHS250x600的箱梁有机结合成整体，形成了一个1300×600高的巨型矩形截面，正好满足了结构工程师所要求的竖向刚度，实现了最初的设计理念。
How to increase the stiffness of the stairs? The usual solution is to use the handrails as the structural members, such as Yangpu Riverside Green Hill. But the architect pursues a transparent effect and uses glass handrails, so other solutions need to be considered. In the traditional calculation, the ladder beams on both sides are used as rod members with connecting rods. The structure concept is clear, and the force is transmitted directly. But the size of members is relatively large. Therefore, the engineer thought of the idea of “intensive structure”. Integrate the stair sealing plate and step plate into the structural members, which can speed up the on-site construction and reduce pavement. More importantly, the RHS250x600 beams on both sides can be reinforced into a whole huge rectangular section of 1300×600, which just meets the vertical stiffness.
Combined section and deformation diagram
HIDE-TECH
日本建筑结构大师大野博史在其文章《日常的结构：从Hi-tech到Hide-tech》中指出，“作为建筑知觉的表现，是将结构不加隐藏地与其他要素相融合，从而使人完全感觉不到结构存在的方法，并把这种手法称为隐技（Hide-tech）”，其本质是结构的透明化，将建筑的吊顶、门窗立柱、地板参与到结构受力中，成为结构的一部分。在某种意义上说，这是一种集约化的结构设计概念，尤其是对于小型建筑，集约化的设计理念给与了建筑师最大的可用空间，满足了这类建筑近乎苛刻的构件尺度要求。
In his article “daily structure: from Hi-tech to Hide-tech”, Japanese architectural structure master Hiroshi Ono pointed out that “as the expression of architectural perception, it is a method to integrate the structure with other elements without hiding, so that people can not feel the existence of the structure at all, and this method is called Hide-tech”. Its essence is the transparency of the structure, which makes the ceiling, the door,the window columns and floor become a part of the structure. In a sense, it is a kind of intensive structural design concept, especially for small buildings. It could gives architects the largest available space and meets the almost extreme requirements of such buildings.
对于结构工程师来说，如何与建筑师有效沟通，在设计时，从建筑、装饰、施工、尺度等多角度思考，采用集约化的设计理念，辅佐以高科技的赋能，以前瞻性、整体性思维方式完成这一类的高品质小型建筑，也是结构工程师所需要关注的方向。
For structural engineers, how to communicate with architects, from the perspective of architecture, decoration, construction, scale, etc., using the intensive design concept, assisted by high-tech empowerment, forward-looking, holistic way, is also the direction that structural engineers need to pay attention to.
LIVE VIEW
特别鸣谢上海史狄尔建筑减震科技有限公司在减振设计中给予的宝贵支持
ganggouren
