| With the transition of construction industry from"mainly constructing new building"to"constructing new building on a par with reconstructing old building"in our country, research on design and construction methods of outer-jacketing structure for adding stories around the existing building begins to draw people's attention gradually. In order to assure the original building work as usual, the design idea of"self-supporting reinforced concrete floor during construction"is put forward. The design idea of"self-supporting reinforced concrete floor during construction"is applied to the reconstruction (extension) project of Suifenhe Qingyun Market. In this project, steel truss of steel-truss-concrete composite beam is made of channel welded together. Channel section of both the top chord and the bottom chord is relative bigger, which accounts for 40% of depth of the column. In addition, prestressed reinforcements need to go through the column, and flared pipe occupies a part of space. All these make it difficult to lay out main reinforcements in column. If channels in steel truss are replaced by circular steel tubes, and both tubes and channels are the same in thickness, then the diameter of steel tubes is only half of channel's depth. Thus, the crowded space into the column is relaxed. At the same, the circular steel tube of bottom chord can be served as duct for some prestressed reinforcements. But cave-in failure mode is apt to occur in hollow steel-tube joint. In order to avoid this kind of failure mode, chord is assumed be grouted to increase the cave-in bearing capacity.At present, there is no method to calculate cave-in bearing capacity for grouted-round-steel tube. Therefore, experiment on cave-in bearing capacity of 9 grouted-round-steel tube is carried out. Influence of some factors on cave-in bearing capacity of grouted-round-steel tube is analyzed including ratio of branch tube diameter to main tube diameter, characteristic and value of axial force acting on chord. The experiment result shows: the cave-in bearing capacity will be strengthened with the increase of ratio of branch tube diameter to main tube diameter or pressure is acted on main tube; but axial tension has little effect on the bearing capacity, and failure of grouted-round-steel tube is ductile, so it has great safety margin. In addition to these factors in model experiment, influence of dimension of chord, thickness of chord's wall, strength of hardened cement pastes and strength of chord steel on cave-in bearing capacity is analyzed in numerical simulated experiment. Based on model experiment and simulated experiment, mechanical property of grouted-round-steel tube in cave-in failure mode is analyzed, then, the formula of cave-in ultimate bearing capacity of grouted-round-steel tube is established.N-joint is widely used in grouted-round-steel tube truss, but there are no systemic researches on its design formula of anti-punching shear bearing capacity, cave-in ultimate bearing capacity and shear bearing capacity. Therefore, experiment on cave-in bearing capacity of 8 N-joints of grouted-round-steel tube truss is carried out. The experiment result shows: anti-punching shear bearing capacity will be strengthened with the increase of diameter ratio of web member to chord; axial press force on chord will enhance cave-in ultimate bearing capacity of grouted-round-steel tube; shear bearing capacity is strengthened for the interaction of chord with the grout. At the same time, numerical simulation with finite element method (FEM) method is done for anti-punching shear failure of N-joint in grouted-round-steel tube truss. Dsign formula of anti-punching shear bearing capacity is proposed by using the least square method; design formula of cave-in ultimate bearing capacity of N-joint is the same as that of T-joint; the capacity superposition of chord and the grout is regarded as the shear bearing capacity.Self-weight of prestressed encased steel-truss-concrete composite beam is the governing weight of building floor, so open web grouted-round steel-truss-concrete composite beam is assumed to replace encased steel-truss-concrete composite beam. There is no reported method about performance, failure mechanism, flexural capacity and displacement of open web grouted-round steel-truss-concrete composite beam. Therefore, model experiment of 4 open web grouted-round steel-truss-concrete composite beams is carried out. During the experiment, effect of some key parameters on flexural capacity and rigidity of composite beam is studied including section of upper chord and bottom chord of steel tube, concrete around upper steel tube. Moreover, the whole failure history of these 4 beams is reported. At the same time, numerical simulation experiment of composite beam is done with FEM. Besides the parameters of model experiment, effect of other more parameters on performance of composite beam is considered including vertical web and inclined web member, distance between nodes, height, angle between inclined web and horizontal chord, and length of solid web beam.The outer-jacketing frame for storey adding is rigid on the top and flexible on the bottom, and the slenderness ratio of the column in the first floor is bigger. So how to ensure the structure be in elastic state under frequent earthquake, no yielding under design earthquake and no collapse under infrequent earthquake has been the focus of people's attention. Combined with the characteristics of outer-jacketing prestressed concrete frame, based on the large-scale finite element method software ANSYS, making use of parameterized design language APDL, program for calculating internal force and placing reinforcement of outer-jacketing concrete frame with prestressed grouted-round steel-truss-concrete composite beam is compiled. All these work have be made reference to Technical specification for steel reinforced concrete composite structures(JGJ 138-2001), Code for seismic design of buildings(GB 50011-2001), Technical specification for concrete structures of tall building(JGJ 3-2002) and Code for design of concrete structures(GB 50010-2002). Based on the plane rod model, by using of IDARC nonlinear analysis programme, the seismic response of outer-jacketing prestressed concrete frames for storey adding with design earthquake group one, two and three, situated in Classâ… ,â…¡andâ…¢soil are analyzed under different earthquake waves in seismic-intensity-7 and seismic-intensity-8 zones. In these cases, the span of frame is 16 m, structural height of the first floor is 7.5m, 11m, 14.5m and 18m separately, and the storey height is 4m with 2, 4, 6, 8 and 10 storeies seperately.Design and construction suggestions on outer-jacketing prestressed concrete frame for storey adding with prestressed grouted-round steel-truss-concrete composite beam are proposed, including general principles, general requirements, structural types, earthquake-resistant grade, limit axial force ratio of column, types of structural material and member section, constitution requirements and suggested design steps.
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